Content data judging apparatus6829367Abstract Content data is judged to determine whether data prepared by a digital device were altered by performing an authentication process using a medium on which content data are recorded; reading the content data from the medium; embedding, in the content data, data for verifying the pertinent content; extracting, from the content data, the data for verifying the pertinent contents; using the results of the extraction to determine whether the content data were altered. Preferably, the means includes means for identifying any portion containing altered data. Claims What is claimed is: Description FIELD OF THE INVENTION
TABLE 1
Table 1: Rules representing the relationship of DCT coefficients:
When the bit value of data corresponding to a pair is 1:
(A.sub.1 < A.sub.2 && B.sub.1 < B.sub.2 && C.sub.1 <
C.sub.2).vertline..vertline. (rule 1-1)
(A.sub.1 > A.sub.2 && B.sub.1 > B.sub.2 && C.sub.1 <
C.sub.2).vertline..vertline.
(A.sub.1 < A.sub.2 && B.sub.1 > B.sub.2 && C.sub.1 >
C.sub.2).vertline..vertline.
(A.sub.1 > A.sub.2 && B.sub.1 < B.sub.2 && C.sub.1 >
C.sub.2
When the bit value of data corresponding to a pair is 0:
(A.sub.1 < A.sub.2 && B.sub.1 < B.sub.2 && C.sub.1 >
C.sub.2).vertline..vertline. (rule 1-2)
(A.sub.1 > A.sub.2 && B.sub.1 < B.sub.2 && C.sub.1 <
C.sub.2).vertline..vertline.
(A.sub.1 < A.sub.2 && B.sub.1 > B.sub.2 && C.sub.1 <
C.sub.2).vertline..vertline.
(A.sub.1 > A.sub.2 && B.sub.1 > B.sub.2 && C.sub.1 >
C.sub.2
wherein in the rules 1-1 and 1-2, X&&Y means both conditions X and Y are satisfied, and XIIY means either condition X or Y is satisfied. Assume that, as is shown in FIG. 9A, the bit value of the data corresponding to pair I is 1, and the values of the mutually corresponding DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) in the two DCT blocks (blocks 1 and 2) of pair I are 4, 4, 2, 3, 4 and 5, 5, respectively. Since the relationship of the values of these DCT coefficients is A.sub.1 =A.sub.2, the rules 1-1 and 1-2 are not satisfied. Therefore, as is shown by the numeral enclosed in the circle in FIG. 9B, the embedding section 30 increments the value of A.sub.2 and embeds bit 1 of the data, so that the relationship of the values of the mutually corresponding DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) satisfies condition (A.sub.1 <A.sub.2 &&B.sub.1 <B.sub.2 &&C.sub.1 <C.sub.2) in rule 1-1. Specifically, if the values of the DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) do not satisfy rule 1-1, the DCT coefficients are adjusted so that the relationship of these DCT coefficients constantly satisfies condition (A.sub.1 <A.sub.2 &&B.sub.1 <B.sub.2 &&C.sub.1 >C.sub.2) in rule 1-1, and bit of 1 of data is embedded. Further, assume that, as is shown in FIG. 10, the bit value of the data corresponding to pair i is 1, and the values of the mutually corresponding DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) in the two DCT blocks (blocks 1 and 2) of pair i are 3, 5, 6, 3, 5 and 4, respectively. The relationship of the values of these DCT coefficients satisfies condition (A.sub.1 <A.sub.2 &&B.sub.1 >B.sub.2 &&C.sub.1 >C.sub.2) in rule 1-1. Therefore, in this case the embedding section 30 does not change the values of the DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) in the two DCT blocks (blocks 1 and 2) of pair i. FIG. 11 is a diagram showing a table that the embedding section 30 (FIG. 2 or 3) uses when embedding data in DCT blocks. In FIG. 11, an embedded data bit number is shown in order to indicate that the embedded data were scrambled. This number not used during the actual processing. A further explanation will be given, while referring to FIG. 11, for the previously described embedding processing performed by the embedding section 30. The embedding section 30 correlates two adjacent DCT blocks, each (FIGS. 7A to 7C) composed of 12288 DCT blocks obtained from image data comprising 1024.times.768 pixels (FIGS. 5 and 6A to 6C), and provides 6144 pairs of DCT blocks. The embedding section 30 receives 96 bits of data from the embedded data generator 20 (FIG. 2), and scrambles the data using a random number produced with a key received from the key information DB 22. The embedding section 30 uses the following method to unrepetitively correlate each of the bit values (1 and 0) of the scrambled 96-bit data with 64 of the 6144 pairs, and enters the results in the embedded data assignment column in the table in FIG. 11. Embedded Data Correlation Method As is shown in FIG. 11, since each bit of the 96-bit data are scrambled in a different order correlates with one of 96 sets of sequential pairs, for example, the seventh bit (1) of the data is assigned to the fifth pair and the 160th pair. Similarly, 6144 pairs are divided into 0.64 sets.times.96 pairs, and individual bits of 96-bit data are correlated with the 96 pairs in each set in a different order for each set. For example, the first to the fourth bits of the 96-bit data are correlated with the eleventh, the fifth, the 31st and the ninth pairs in the first set that includes the first to the 96th pairs, and with the 99th, the 126th and the 153rd pairs in the second set that includes the 97th to 192nd pairs (see FIG. 18). The embedding section 30 uses the generated random number to determine which DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) are to be extracted from two DCT blocks (blocks 1 and 2) in each pair, as is shown in FIG. 8. The values of the extracted DCT coefficients are written in blocks 1 and 2 of the coefficient columns in the table. As is described above, the 8.times.8 DCT coefficients are extracted by embedding section 30 are not constant for every pair. When the above processing is completed, the embedding section 30 adjusts the values of the DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) entered in the block 1 and 2 columns of the table, so that the DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) selected from the DCT blocks (blocks 1 and 2) for each pair represent the bit values in the embedded data assignment column of the table in accordance with rules 1-1 and 1-2 in table 1. The embedding section 30 again performs Huffmann coding for the DCT coefficients (DCT blocks) of luminance element Y and the chroma elements Cr and Cb in which the data are embedded, and obtains compressed image data that can be decompressed using the JPEG method. The resultant image data are output to the image DB 24 (FIG. 2). Components of Embedding Section 30 The components of the embedding section 30 will be described while again referring to FIGS. 3 and 4. Decoder 300 Under the control of the controller 26 (FIG. 2), the decoder 300 (FIG. 3) performs Huffmann decoding for the JPEG data received via the camera IF 104 or the memory card IF 106. Then, from among the resulting three DCT coefficients (DCT blocks) that are obtained, the decoder 300 outputs to the encoder 304 the DCT coefficients (DCT blocks) for the chroma elements Cr and Cb, and outputs to the data embedding portion 32 the DCT coefficient (DCT block) for the luminance element Y. Data Embedding Portion 32 The data embedding portion 32 embeds the data that were explained while referring to FIGS. 7 to 11. The individual components of the data embedding portion 32 will now be described while referring to FIG. 4. Image Divider 320 The image divider 320 divides the DCT coefficient (DCT block: FIG. 7A) of luminance signal Y received from the decoder 300 into the pairs in FIGS. 7B and 7C, and outputs the pairs to the coefficient operator 328. Random Number Generator 322 The random number generator 322 uses the 16-bit linear congruence method to generate a random number RN by using, for example, a 64-bit key received from the key information DB 22 (FIG. 2). The obtained random number is transmitted to the positioning portion 324 and the scrambling portion 326. Positioning Portion 324 For each pair obtained by the image divider 320, the positioning portion 324 determines which DCT coefficients in the two DCT blocks (blocks 1 and 2) are to be selected by using the random number RN received from the random number generator 322 (locations of selected DCT coefficients: FIG. 8). The position data that indicate the locations of the determined DCT coefficients are output to the coefficient operator 328. Scrambling Portion 326 The scrambling portion 326 uses the random number RN received from the random number generator 322 to scramble the 96-bit data received from the embedded data generator 20 (FIG. 2). As a result of the scrambling process, while 96 bits are regarded as one repetition unit, the scrambling portion 326 outputs, to the coefficient operator 328, data (hereinafter referred to as scrambled embedded data, or simply as embedded data) that include the 64 repetition units, each of which includes, in different orders, all 96 bits of the embedded data. Embedding Table Preparation Process Performed by Coefficient Operator 328 The coefficient operator 328 first prepares the embedding table shown in FIG. 11. Specifically, first, the coefficient operator 328 extracts the DCT coefficients (FIG. 8) from the two DCT blocks (blocks 1 and 2 in FIG. 7B) of each pair in accordance with the position data received from the positioning portion 324. Then, the coefficient operator 328 enters the DCT coefficients in the block 1 and 2 columns in the embedding table (FIG. 11), and enters the embedded data received from the scrambling portion 326 in the embedded data assignment column. Data Embedding Process Performed by Coefficient Operator 328 FIG. 12 is a flowchart showing the process (S10) performed by the coefficient operator 328 in FIG. 4 to embed data in the DCT block pair. Next, the coefficient operator 328 embeds, in each DCT coefficient (DCT block) pair, the bits of corresponding data in the table (FIG. 11), and outputs, to the encoder 304 (FIG. 3), the data as the DCT coefficient Y' of the luminance element. As is show n in FIG. 12, at step 100 (S100), the coefficient operator 328 sets, to an initial value of 1, variable i represents the 6144 pairs. At step 102 (S102), the coefficient operator 328 extracts DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) for the i-th pair from the block 1 and 2 columns in the table (FIG. 11), and also extracts embedded bits from the embedded data assignment column. At step 104 (S104), the coefficient operator 328 determines whether the value of the embedded bit extracted at step 102 is 1. When the bit value is 1, program control advances to S106, and when the bit value is 0, program control moves to S110. At step 106 (S106), the coefficient operator 328 determines whether the object DCT coefficients satisfy rule 1-1 in table 1, i.e., whether they represent the value 1. When the DCT coefficients satisfy rule 1-1, as shown in FIG. 10, program control moves to S114. In the other cases, program control goes to S108. At step 108 (S108), the coefficient operator 328 adjusts the object DCT coefficients so that they satisfy rule 1-1. At step 110 (S108), the coefficient operator 328 determines whether the object DCT coefficients satisfy rule 1-2 in table 1, i.e., whether they represent the value 0. When the DCT coefficients satisfy rule 1-2, program control moves to S114. In the other cases, program control goes to S112. At step 112 (S112), the coefficient operator 328 adjusts the object DCT coefficients so that they satisfy rule 1-2. At step 114 (S114), the coefficient operator 328 determines whether the value of variable i is 6144, i.e., whether the data embedding process was completed for all the pairs. When all the data were embedded, the process is thereafter terminated. In the other cases, the variable i is incremented by one, and program control returns to S102. Encoder 304 The encoder 304 (FIG. 3) performs Huffmann coding for the DCT coefficients of chroma elements Cr and Cb received from the decoder 300 and the DCT coefficients Y' of the luminance element Y, in which the data are embedded and received from the data embedding portion 32. The encoder 304 outputs the resultant data to the image DB 24. Extraction Section 40 FIG. 13 is a diagram showing the arrangement of the extraction section 40 in FIG. 2. FIG. 14 is a diagram showing the arrangement of an embedded data extraction portion 42 in FIG. 13. As is shown in FIGS. 13 and 14, the extraction section 40 includes a decoder 400, an image divider 402, an encoder 404, an image synthesizer 406, the embedded data extraction portion 42, an alteration detector 44 and a clustering portion 46. The embedded data extraction portion 42 is constituted by a random number generator 420, a positioning portion 422, an extraction order generator 424, a correlating portion 426 and a data extractor 428. Outline of Extraction Section 40 If an alteration is added to one part or all of the JPEG data in which the embedding section 30 has embedded data, as described while referring to FIGS. 7 to 12, the relationship of the values of the DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2) which mutually correspond to each other in the two DCT blocks (blocks 1 and 2 in FIG. 7B) for each pair and were used to embed the data, does not indicate the value of a bit embedded during the process in FIGS. 9A, 9B and 10 in accordance with rules 1-1 and 1-2 in table 1. The components of the extraction section 40 use the property of the JPEG data, including the embedded data, to determine whether the JPEG data generated by the embedding section 30 were altered. Further, if the JPEG data were altered, the extraction section 40 determines and displays an altered portion of the image data (FIG. 5). Details of Extraction Section 40 The processing performed by the extraction section 40 will now be described in detail while referring to FIGS. 15 to 22. As is described above, the embedding section 30 (FIGS. 2 and 3) uses the random number generated using a key received from the key information DB 22 to obtain, for each pair, the locations of the DCT coefficients used to embed data. Therefore, the extraction section 40 can use the same key as the embedding section 30 to obtain, for DCT blocks (blocks 1 and 2 in FIG. 8) for each pair, the DCT coefficients that were used to embed data. In addition, the embedding section 30 uses the random number generated using a key received from the key DB 22 to scramble the individual 96 bits of the embedded data and to correlate these bits with the pairs. Therefore, the extraction section 40 can use the same key as the embedding section 30 to determine which bit of the 96-bit embedded data is correlated with each pair. The extraction section 40 uses the same key as the embedding section 30 to obtain, for two DCT blocks (blocks 1 and 2) for each pair, DCT coefficients used to embed bits. In addition, the extraction section 40 extracts the bit value (1 or 0) of the data embedded in each pair, in accordance with which rule 1-1 and rule 1-2 in table 1 are satisfied by the relationship of the values of the mutually corresponding DCT coefficients used for bit embedding. Next, the extraction section 40 uses the same key as the embedding section 30 to determine which bit of the embedded data corresponds to the bit value of the embedded data that are extracted from each pair. FIG. 15A is a diagram showing an example image obtained by decompressing JPEG data in which data are embedded by the embedding section 30 (FIGS. 2 and 3). FIG. 15B is a diagram showing a portion to be altered in the image in FIG. 15A. FIG. 15C is a diagram showing the image after it is altered. Assume that, as is shown in FIGS. 7 to 12, the embedding section 30 embeds, in the JPEG data, data obtained from the image data in FIGS. 5 and 6A to 6C; that a third party decompresses the resultant JPEG data to obtain the image of the car in FIG. 15A, and alters a portion indicated by the broken line in FIG. 15B to generate an image in which details of the car are partially deleted or corrected as is shown in FIG. 15C; and that the image data are again compressed and encoded using the JPEG method and the resultant data are used to replace the original JPEG data. In this case, since only one small part of the image data was altered, the values of many of the 64 values extracted from the 64 pairs correlated with the same bit of embedded data will be those that were held before the alteration, and only a small number of pairs will have values that were updated by the alteration. The extraction section 40 uses such a property, accompanied by the alteration of one part of an image, to accept a majority bit decision while the bits extracted from the individual pairs are correlated with the bits of the embedded data. Then, if a value of 1 (or 0) is extracted from the majority of the 64 pairs correspond to the k-th bit of the embedded data and a value of 0 (or 1) is extracted from the minority of the pairs, it is assumed that the embedding section 30 embedded a value of 1 (or 0) as the k-th bit in the 64 pairs. That is, the extraction section 40 accepts a majority bit decision based on the values of the extracted bits of embedded data, and assumes that the value held by the majority of pairs was the bit data value embedded in all the pairs by the embedding section 30. In addition, the extraction section 40 assumes that an alteration was added to a pair from which the value extracted corresponds to the value held by the minority of the pairs. FIG. 16 is a diagram showing an example where a binary image indicating altered portions is synthesized with the original image. As is shown in FIG. 16, the extraction section 40 synthesizes the original image in FIG. 5 with the binary image (the center shaded area and the shaded area on the license number plate in FIG. 16) that indicates pairs to which alterations were added, and displays the altered areas on the display device 100 (FIG. 1). FIG. 17 is a diagram showing an example where the original image is synthesized with an image obtained using a clustering process and that indicates the extent of the alterations. As is shown in FIG. 17, the extraction section 40 performs the clustering process to obtain an image that indicates the extent of the tessellated areas of the binary image in FIG. 16, and synthesizes this image with the original image in FIG. 5 to display the altered areas on the display device 100. To perform this process, first, the extraction section 40 performs Huffmann decoding for the JPEG data received from the image data DB 22, and obtains three types of DCT coefficients (DCT blocks). The extraction section 40 then extracts 12288 DCT coefficients (DCT blocks Y') for luminance element Y, and forms 6144 pairs of adjacent DCT coefficients, as shown in FIGS. 7B and 7C. The extraction section 40 determines which of the rules 1-1 and 1-2 is satisfied by the relationship of the DCT coefficients used to embed data in the two DCT blocks (blocks 1 an 2 in FIG. 8) included in each pair. The extraction section 40 then extracts the bit value (1 or 0) of the data (second embedded data) embedded in each pair. If the DCT coefficients correspond to the two DCT blocks (blocks 1 and 2) are equal (e.g., A.sub.1 =A.sub.2), neither rule 1-1 nor rule 1-2 applies, so the extraction section 40 determines that an alteration was added to the pertinent pair. To simplify the following explanation, an example where the corresponding DCT coefficients are not equal is used. FIG. 18 is a diagram showing the bit values extracted from the pairs in the JPEG data, by the extraction section 40, when no alteration or error was added to the JPEG data generated by the embedding section 30 (FIGS. 2 and 3). The extraction section 40 extracts bits of the embedded data from the pairs (second image blocks), in the JPEG data, that were generated by the embedding section 30 and to which no alteration or error was added. When the values of the bits are rearranged in accordance with the correlation of the bits with the pairs, the values of all the extracted bits correspond to the embedded data match. FIG. 19 is a diagram showing bit values extracted from the pairs in the JPEG data, by the extraction section 40, when an alteration or error is added to JPEG data generated by the embedding section 30 (FIGS. 2 and 3). The extraction section 40 extracts the bits of the embedded data from the pairs (second image blocks), in the JPEG data, that were generated by the embedding section 30 and to which an alteration or an error was added. When the bit values of the embedded data are rearranged in accordance with the correlation of the bits of the data with the pairs in the same manner as in FIG. 18, as shown by the extracted values enclosed by thick frames in FIG. 19, the bits extracted from the minority of the pairs, for which an alteration was performed, have different values from the bits extracted from the non-altered, majority of pairs. As a result, a match is not obtained. The extraction section 40 thus assumes that the bit values obtained by the majority bit decision are the values of the data embedded by the embedding section 30. FIG. 20 is a diagram showing an example binary image. In this example, the extraction section 40 (FIGS. 13 and 14) uses the JPEG data altered as is shown in FIG. 15 to examine pairs that are altered as is shown in FIG. 19, and the location in the image of the altered pairs is indicated in the binary image. For the sake of convenience while giving the explanation, the example in FIG. 20 does not always match the example in FIG. 15. As is shown in FIG. 20, the extraction section 40 generates a binary image that indicates the location on the screen of the pairs from which bits were extracted whose values differ from the value selected by the majority bit decision. As is described above while referring to FIG. 16, the binary image generated by the extraction section 40 is synthesized with the original image, and the obtained image is displayed on the display device 100 (FIG. 1). FIGS. 21A to 21D are diagrams showing an example clustering image. In this example, the extraction section 40 (FIGS. 13 and 14) uses the JPEG data that are altered as in FIG. 15 to determine the pairs altered as in FIG. 19, and the extent of the areas occupied by the pairs is indicated by the clustering image. For the sake of convenience while giving the explanation, the examples in FIGS. 21A to 21D do not always match the example in FIG. 15. As is shown in FIGS. 21A and 21C, the extraction section 40 determines the extent of the areas on the screen occupied by the pairs from which bits were extracted whose values differ from the value selected by the majority bit decision, and generates the clustering image shown in FIGS. 21B and 21D. As is described above while referring to FIG. 17, the clustering image generated by the extraction section 40 is synthesized with the original image, and the resultant image is displayed on the display device 100 (FIG. 1). Components of Extraction Section 40 The components of the extraction section 40 will be described while again referring to FIGS. 13 and 14. Decoder 400 Under the control of the controller 26, the decoder 400 performs Huffmann decoding for the JPEG data received from the image DB 24. Then, from among the obtained three types of image elements, the decoder 400 outputs chroma elements Cr and Cb to the encoder 404, and outputs the luminance element Y' to the image divider 402. Image Divider 402 The image divider 402 divides the received luminance element Y' into DCT coefficients (DCT blocks), and outputs the DCT coefficients (DCT blocks) to the embedded data extraction portion 42. Embedded Data Extraction Portion 42 The embedded data extraction portion 42 correlates each two of the DCT blocks for the luminance element Y' that are received from the image divider 402 and forms the pairs (FIGS. 7B, 7C and 8) used by the embedding section 30. The embedded data extraction portion 42 extracts the values of the data bits embedded in the pairs, and outputs the bit values to the alteration detector 44 as the extracted data in FIGS. 18 and 19. In addition, the embedded data extraction portion 42 outputs to the encoder 404, unchanged, the received Luminance element Y' as a luminance element Y. Correlating Portion 426 The correlating portion 426 (FIG. 14) correlates each two adjacent DCT blocks (blocks 1 and 2: FIG. 7B) in 12288 DCT coefficients (DCT blocks) received from the image divider 402, and generates 6144 pairs of DCT coefficients (FIGS. 7B and 7C). Then, the correlating portion 426 outputs the 6144 pairs to the data extractor 428. That is, the correlating portion 426 corresponds to the image divider 320 (FIG. 4) of the embedding section 30 (FIGS. 2 and 3), and, as does the image divider 320, generates pairs of DCT blocks. Random Number Generator 420 The random number generator 420 receives, from the key information DB 22 (FIG. 2), the same key as is used by the embedding section 30 for embedding data, and uses that key and the same method as is used by the embedding section 30 to generate a random number RN. The random number generator 420 outputs the obtained random number RN to the positioning portion 422 and to the extraction order generator 424. That is, the random number generator 420 corresponds to the random number generator 322 (FIG. 4) of the embedding section 30, and uses the same key and the same method as those used by the random number generator 322 to generate the random number RN. Positioning Portion 422 The positioning portion 422 uses the received random number RN to generate position data indicating which DCT coefficients, of the two DCT blocks (blocks 1 and 2) included in each pair, were used by the embedding section 30 to embed data. The positioning portion 422 then outputs the position data to the data extractor 428. That is, the positioning portion 422 corresponds to the positioning portion 324 of the embedding section 30, and uses the same random number as the one used by the positioning portion 324 to generate the same position data as those generated by the positioning portion 324. Extraction Order Generator 424 As is described above, 6144 pairs transmitted from the correlating portion 426 to the data extractor 428 are formed into sets, each of which includes 96 pairs. In an order differing for each set, each bit of the 96-bit embedded data is individually correlated with one of the 96 pairs in each set. The extraction order generator 424 uses the received random number RN to generate order data indicating the order in which the 96 bits of the embedded data are individually correlated with the pairs in each of the pair sets. The extraction order generator 424 then outputs the order data to the data extractor 428. For the two DCT blocks (blocks 1 and 2) included in each pair, the data extractor 428 determines which of the rules 1-1 and 1-2 is satisfied by the relationship of the values of the mutually corresponding DCT coefficients (FIG. 8), which are indicated by the position data received from the positioning portion 422. The data extractor 428 then extracts the values of the bits of data embedded in each pair. Furthermore, the data extractor 428 rearranges the extracted bit values in the order corresponding to that expressed by the order data received from the extraction order generator 424, and generates the extraction data in FIGS. 18 and 19. The data extractor 428 then outputs the extraction data to the extraction order generator 424. The bit extraction process performed by the data extractor 428 will be further described while referring to FIG. 22. FIG. 22 is a flowchart showing the process performed by the data extractor 428 in FIG. 14 when extracting data bits embedded in the individual pairs. As is shown in FIG. 22, at step 120 (S120), for initialization, the data extractor 428 loads a 1 into variable i, which represents the 6144 pairs. At step 122 (S122), the data extractor 428 extracts, as an object, the i-th pair indicated by variable i. At step 124 (S124), for the two DCT blocks (blocks 1 and 2) included in the extracted pair, the data extractor 428 determines which of the rules 1-1 and 1-2 is satisfied by the relationship of the DCT coefficients indicated by the position data received from the positioning portion 422. When the relationship corresponds to rule 1-1, bits of value 1 are extracted from the i-th pair. When the relationship corresponds to rule 1-2, bits of value 0 are extracted from the i-th pair. Further, the data extractor 428 uses the order data received from the extraction order generator 424 to determine a bit of embedded data corresponds to the value of the extracted bit. The values (1 and 0) of the extracted bits are entered at the obtained locations in the extracted data diagrams in FIGS. 18 and 19. At step 126 (S126), the data extractor 428 determines whether the number held by variable i is 6144, i.e., whether the bit extraction process was completed for all the pairs. When the bit extraction was completed, the processing is thereafter terminated. In the other cases, the variable i is incremented by one and program control returns to S122. When the bit extraction process to extract the data in FIGS. 18 and 19 was completed for all the pairs, the data extractor 428 accepts a majority bit decision based on the 64 values that were extracted for each of the 96 corresponding embedded data bits, and assumes the data was embedded by the embedding section 30 (FIGS. 2 and 3). The data extractor 428 then outputs each pair as luminance element Y to the encoder 404. Encoder 404 The encoder 404 (FIG. 3) performs Huffmann coding for the chroma elements Cr and Cb received from the decoder 400 and the luminance element Y received from the data extractor 428, and generates JPEG data. The encoder 404 outputs the JPEG data to the image synthesizer 406. Alteration Detector 44 The alteration detector 44 uses the extraction data (FIGS. 18 and 19) received from the data extractor 428 to generate the binary image in FIG. 20, and then outputs the binary image to the image synthesizer 406. Clustering Portion 46 Upon receiving the binary image from the alteration detector 44, the clustering portion 46 generates a clustering image (FIG. 21) by which the extent of an alteration is indicated, and outputs the clustering image to the image synthesizer 406. Image Synthesizer 406 Under the control of the controller 26, the image synthesizer 406 decompresses the JPEG data received from the encoder 404, generates an image shown in FIG. 5 or 15C, and displays the produced image, unchanged, on the display device 100 (FIG. 1). Or, the image synthesizer 406 synthesizes the binary image received from the alteration detector 44, or the clustering image received from the clustering portion 46, with the image obtained by decompression, and generates the image shown in FIG. 16 or 17. The image synthesizer displays the altered portion in the image on the display device 100. Or, the image synthesizer 406 displays, unchanged, the binary image received from the alteration detector 44, or the clustering image received from the clustering portion 46, on the display device 100 to indicate the extent of the image alteration. Data Embedding Process Performed by Image Alteration Determination Apparatus 1 The overall data embedding process performed by the image alteration determination apparatus 1 will now be described while referring to FIG. 23. FIG. 23 is a flowchart showing the data embedding process (S20) performed by the image alteration determination apparatus 1 in FIG. 1. At step 200 (S200), the decoder 300 (FIG. 3) performs Huffmann decoding for the JPEG data received via the camera IF 104, and outputs, to the data embedding portion 32, 12288 DCT coefficients (DCT blocks) for luminance element Y. The image divider 320 divides the received DCT coefficients (DCT blocks: FIG. 7A) into 6144 pairs (FIGS. 7B and 7C), and outputs the pairs to the coefficient operator 328. The random number generator 322 generates a random number RN using a key received from the key information DB 22 (FIG. 2), and outputs the random number RN to the positioning portion 324 and the scrambling portion 326. The positioning portion 324 uses the received random number RN to generate position data that indicates the locations of the DCT coefficients used for data embedding. The positioning portion 324 then- outputs the position data to the coefficient operator 328. The scrambling portion 326 uses the random number RN to scramble the 96-bit data received from the embedded data generator 20 (FIG. 2), and then outputs the scrambled data to the coefficient operator 328. At step 10 (S10), first, based on the position data received from the positioning portion 324, the coefficient operator 328 (FIG. 4) selects, for each pair, DCT coefficients (A.sub.1, A.sub.2, B.sub.1, B.sub.2, C.sub.1 and C.sub.2 : FIG. 8) that are the data embedding objects. Furthermore, the coefficient operator 328 correlates each pair with one bit of the embedded data received from the scrambling portion 326, and prepares the embedding table in FIG. 11. In addition, the coefficient operator 328 sequentially extracts, from the table, the object DCT coefficients and the bits to be embedded, and embeds the bits of the data in the individual pairs, as shown in FIGS. 9A, 9B and 10, in accordance with the rules 1-1 and 1-2 in table 1. When bits were embedded in all the pairs, at step 202 (S202), the encoder 304 (FIG. 3) performs Huffmann coding for the DCT coefficients (DCT blocks) for luminance element Y and the DCT coefficients for the other elements received from the decoder 300, and generates the JPEG data. The encoder 304 then outputs the JPEG data to the image DB 24 (FIG. 2). The JPEG data from the embedding, section 30 are stored and managed in the image DB 24. Data Extracting Process Performed by Image Alteration Determination Apparatus 1 The overall data extracting process performed by the image alteration determination apparatus 1 will now be described while referring to FIG. 24. FIG. 24 is a flowchart showing the data extracting process (S22) performed by the image alteration determination apparatus 1 in FIG. 1. At step 220 (S220), the decoder 400 (FIG. 13) performs Huffmann decoding for JPEG data supplied from the image DB 24, and outputs luminance element Y' to the image divider 402. The image divider 402 divides the luminance element Y' into 12288 DCT coefficients (DCT blocks), and outputs them to the embedded data extraction portion 42. At the embedded data extraction portion 42, the correlating portion 426 correlates each set of two adjacent DCT coefficients (DCT blocks: FIG. 7A) to prepare 6144 pairs (FIGS. 7B and 7C), and outputs the pairs to the data extractor 428. The random number generator 420 (FIG. 14) generates a random number RN using a key received from the key information DB 22 (FIG. 2), and outputs the number to the positioning portion 422 and the extraction order generator 424. The positioning portion 422 uses the random number RN received from the random number generator 420 to generate position data representing the locations of the DCT coefficients used for data embedding. The positioning portion 422 then outputs the position data to the data extractor 428. The extraction order generator 424 uses the random number RN received from the random number generator 420 to generate order data representing the correlation of each pair with an embedded data bit. The extraction order generator 424 then outputs the order data to the data extractor 428. At step 12 (S12), as is shown in FIG. 22, the data extractor 428 sequentially extracts pairs, and extracts the values of the bits embedded in the pairs, in accordance with the rule, 1-1 or 1-2, that is satisfied by the relationship of the values of the DCT coefficients of the two DCT blocks (blocks 1 and 2) specified by the position data received from the positioning portion 422. Furthermore, the data extractor 428 uses the order data received from the extraction order generator 424 to determine which bit in the embedded data corresponds to the extracted bit value. The data extractor 428 writes the extracted bit value (1 or 0) at the position in the extracted data (FIGS. 18 and 19) obtained as the result of the determination. When the values of the bits were extracted from all the pairs, at step 222 (S222), for the extracted data in FIGS. 18 and 19, the data extractor 428 accepts a majority bit decision based on the 64 values extracted for the corresponding bits of the 96-bit data. As a result, the data extractor 428 makes an assumption as to the data embedded by the embedding section 30 (FIGS. 2 and 3). Furthermore, the encoder 404 (FIG. 13) performs Huffmann coding for the chroma elements Cr and Cb received from the decoder 400 and the luminance element Y received from the embedded data extraction portion 42, and generates the JPEG data. The encoder 404 then outputs the JPEG data to the image synthesizer 406. At step 224 (S224), the alteration detector 44 generates the binary image shown in FIG. 20 using the extracted data (FIGS. 18 and 19) received from the data extractor 428, and outputs the binary image to the image synthesizer 406. The clustering portion 46 uses the binary image received from the alteration detector 44 to generate a clustering image (FIG. 21) that indicates the extent of the alteration that was made. The clustering portion 46 then outputs the clustering image to the image synthesizer 406. Under the control of the controller 26, the image synthesizer 406 synthesizes the binary image received from the alteration detector 44, or the clustering image received from the clustering portion 46, with the image obtained by decompression. The image synthesizer 406 then generates the image shown in FIG. 16 or 17, and displays the altered portion of the image on the display device 100. Modification A modification of the embodiment of the present invention will now be described. Image Data Area In the above embodiment, the data in the entire area occupied by the image data is divided into pairs, and all the image data in the area is examined to determine whether it was altered. However, the division into pairs and the alteration determination may be performed for only a part of the image data, or the area in which the division into pairs is effected may not correspond to the area in which the alteration determination is performed. Transformation Method Other Than the DCT Process In the above embodiment, the DCT process is performed to compress and encode image data. However, the alteration determination method of the present invention can be applied not only for the DCT process, but substantially, can also be applied for the compression and encoding of image data by using a spatial or frequency transformation, such as Wavelet transformation, Fourier transformation and FFT (Fast Fourier Transformation), to transform spatial data into frequency data. Embedding Data in a Portion Other Than a Luminance Element In the above embodiment, the data are embedded in the DCT coefficient for the luminance element Y. The alteration determination method of the present invention can also be used for embedding data in chroma elements Cr and Cb. Further, the alteration determination method of the present invention can be applied for other image data, such as RGB image data. Correlation of DCT Blocks In the above embodiment, each set of two adjacent DCT coefficients are correlated with each other. However, using a random number, two DCT coefficients (DCT blocks) can be selected at random from the 12288 DCT blocks and can be correlated with each other to form a pair. As is indicated by the broken line in FIG. 4, the random number generator 322 can supply a random number RN to the image divider 320, which can then use the random number RN to select two DCT coefficients (DCT blocks) to form a pair. As is indicated by the broken line in FIG. 14, the random number generator 420 can supply a random number RN to the correlating portion 426, and the correlating portion 426 can use the random number RN to reproduce a pair that is correlated by the image divider 320. The embedded data scrambling method is not limited to the method used in this embodiment, and a method may be used according to which individual bits of embedded data are assigned to all the pairs a constant number of times. Application for Data Other Than Image Data When the embedding/judging program 2 of the present invention is properly modified, in addition to image data, the program can be used to determine whether portions of such content data as audio data were altered. An explanation will now be given for a case where the present invention is applied for audio data. Audio data can be processed by using sequential sampling points as a block. When, for example, 1024 sets of audio data having a sampling frequency of 44.1 Khz are defined as a block, 44 audio data blocks can be processed in one second. When an FFT is used to transform these audio data blocks into data blocks in a frequency area, data can be embedded in the same manner as in the above embodiment, and an alteration can be detected by using the embedded data. Method for Connecting a Plurality of Alteration Determination Apparatuses 1 FIG. 25 is a diagram showing the arrangement of an alteration determination system 4 where a plurality of image alteration determination apparatuses 1 (1-1 to 1-n), each of which include an image DB 24 (24-1 to 24-n), are connected together. Assume that, as is shown in FIG. 25, the image alteration determination apparatuses 1-1 to 1-n, which respectively include the image DBs 24 (24-1 to 24-n) and the embedding/extraction units 3 (3-1 to 3-n), are connected via the communication device 116 (FIG. 1; not shown in FIG. 25). In order to detect image data alterations, overall management of image data, stored and managed in the image DBs 24-1 to 24-n, and keys is effected using the key information DB 22-1 of the image alteration determination apparatus 1-1; and the keys are distributed to the image alteration determination apparatuses 1-1 to 1-n so that security can be maintained. Content Data Judging Apparatus An explanation will now be given for a content data judging apparatus that is used for a security maintenance system, so that content data prepared by a digital device can be handled as evidence data. The tamper proof technique used in the following explanation is a well known technique for protecting a software/hardware module, including a highly confidential algorithm, from reverse engineering, such as is performed by a disassembler. RC4 is a well known cryptographic algorithm that was devised by Ron Rivest (RSA Data Security Inc.). No explanation will be given for that algorithm. FIG. 26 is a block diagram illustrating a data judging apparatus according to the present invention. A JPEG image acquired by a digital camera 510 can be stored in a storage device (e.g., on a hard disk) via a device driver program 530 (hereinafter referred to simply as a driver), without its validity being compromised by an alteration or a substitution. The validity of the JPEG image data is examined at the PC by an application 550, and the results are displayed. If the JPEG image was altered, the altered portion is identified. It should be noted that the JPEG image acquired by the digital camera 510 is protected by a plurality of authentication processes performed for the components 510 and 520, using a key (Kdc); for the components 520 and 530, using a key (Kpc), and for the components 530 and 540, using a key (Kapp). Since a high level of security is maintained, the suitability of the digital content to serve as evidence can be drastically increased. The PC that executes the driver 530 and the registration application 540 for embedding an electronic watermark may be an electronic watermark embedding apparatus, or the PC that executes the application 550 for extracting an embedded electronic watermark and for identifying an altered portion of the JPEG image may be a dedicated electronic watermark extraction apparatus. Further, the same PC may be used for the embedding and the extraction of an electronic watermark. FIG. 46 is a hardware block diagram illustrating the digital camera 510 and a CF 520 used for the present invention. First, specific common commands (a Request Seed command and a Send Seed command) are defined between the digital camera 510, the CF 520 and the driver 530. Upon receiving these commands, the general apparatus returns an error or enters a time out. The Request Seed command is a command for requesting the transmission of a seed to a client, and the Send Seed command is a command for notifying a client of the transmission of a seed. The authentication is performed by the devices exchanging these commands and determining whether a requested series was returned. The digital camera 510 and the CF 520 use the common key Kdc, which is stored in the ROM area of the digital camera 510. The key Kdc is also encrypted using the key Kcf of the CF 520 and is stored in a NAND area 521 (Readable/writable memory area) of the CF 520 because the CF used by a specific digital camera may also be used by another digital camera. The key Kdc in the CF 520 is held as information indicating with which digital camera the key Kdc is used in the initial state. It should be noted that the key Kdc can be changed during the initialization process. The key Kcf is used to specify the CF 520, which includes a RAM area 525 and the NAND area 521 as memory areas. The RAM area 525 is used temporarily for the exchange of data, and the NAND area 521 is used primarily for the storage of image data and key information. A CPU 522 performs calculations and comparisons for the generation of a random number and for encryption (RC4). The key Kdc is encrypted by using the key Kcf, raw image data (JPEG), the encrypted data obtained from divided image data, the key Kpc, a digital camera ID file, a user ID file, a photo acquisition date, and the serial number of the CF 520 stored in the NAND area 521 of the CF 520. The encrypted key and data stored in the NAND area 521 differ from the data in the RAM area 525, and can not be decoded by reading these data using a normal method. Key databases 560, 570, 580 and 590 are used to manage key information, which is to be stored in the individual devices, that the individual devices use to perform authentication. A digital camera ID and a secret key Kdc are stored in the key database 560, and a user Id and a secret key Kpc are stored in the key database 570. These data bases are used to initialize the CF 520 before it is installed in the digital camera. The initialization process is performed in the following manner. (1) The user ID is stored in the RAM area 525 of the CF 520. (2) The key Kpc is stored in the NAND area 521 of the CF 520. (3) The device ID file is stored in the NAND area 521 of the CF 520. (4) The key Kdc is stored in the NAND area 521 of the CF 520. The keys Kdc and Kpc, which are stored in the NAND area 521, are used to prepare a series that is used by the devices to perform an authentication process. The thus initialized CF 520 and the digital camera perform the authentication process and store data in the following manner. First, an authentication unit 513 in the digital camera 510 and an authentication unit 523 in the CF 520 use the common key Kdc to perform an authentication process. If the authentication process is successful, the digital camera 510 uses an image fetching unit 511 constituted by a CCD, etc., to generate an image signal, and transmits the image signal to an image processor 512. The image processor 512 then reproduces the image signal to obtain image data, and writes the image data in the NAND area 521 of the CF 520. Paralleling this process, each 512 bytes of the image data are encrypted as needed by using the key Kcf and the serial number of the CF 520, and the resultant data are written as encrypted data in the NAND area 521. It is preferable that the ROM area 523 be a tamper proof area. When an image is held in the CF 520, it means that the image data and the encrypted data obtained from the divided image data are stored in the NAND area 521. FIG. 31 is a main flowchart for the data judging method. At step S1000 a JPEG image is generated by the digital camera 510, and program control then goes to step S2000. At step S2000, an authentication step for the components 510 and 520, an authentication process is performed between the digital camera 510 and the CF 520 and the results and the JPEG image are stored in the CF 520. At step S3000, an authentication step for the components 520 and 530, an authentication process is performed between the CF 520 and the driver 530 and the results are transmitted to the components 530 and 540, for an authentication process to be performed at step S4000. At step S4000 an authentication process is performed between the CF driver 530 and the JPEG image registration/storage application 540 and the results are transmitted to the components 540 and 550, for an authentication process to be performed at step S5000. At step S5000, an embedding step for an ID, etc., the results of the authentication processes at steps S2000, S3000 and S4000 are displayed, and an ID and an alteration detection mark are embedded in the JPEG image. At step S6000, a step for the extraction/detection of an ID, etc., the ID and the alteration detection mark are extracted from the JPEG image and the results are displayed. When an alteration is found, the pertinent altered portion is also displayed. FIG. 32 is a flowchart for the authentication process performed at step S2000 between the components 510 and 520. At step S2100, at which an authentication process is performed between the components 510 and 520, the digital camera 510 and the CF 520 use the key. Kdc to perform the authentication process, and output the JPEG image obtained at step S1000 and the results of the authentication process. At step S2200, a step for storing the JPEG image, the JPEG image storage key Kcf is used to store the results obtained at step S2100 and the JPEG image in the CF 520. FIG. 33 is a detailed flowchart for the authentication process performed at step S2100 between the components 510 and 520. First, at step S2100 the CF 520 generates a series (a) of random numbers, and transmits this series to the digital camera 510. At step S2120 the digital camera 510 encrypts the received series (a) using the key Kdc, and generates a series (b). At step S2130 the CF 520 uses the key Kdc to encrypt the random numbers (a) using RC4 (the calculations are performed by the CPU 522 of the CF 520 in FIG. 46), and generates a series (c). At step S2140 the CF 520 compares the obtained series (c) with the series (b) that was obtained by the digital camera 510. When the two series correspond, it is ascertained that the authentication process performed between the digital camera 510 and the CF 520 was successful because the key Kdc was used in common by the two devices. When the two series differ, it is ascertained that the authentication process performed between the digital camera 510 and the CF 520 failed. FIG. 34 is a detailed flowchart for step S2200 at which an image is retained in the CF 520. When the authentication process performed between the digital camera 510 and the CF 520 is successful, the image generated by the digital camera 510 is stored in the CF 520 using the key Kcf. At step S2210, a JPEG image division step, the JPEG image generated by the digital camera 510 is divided to provide strings of 512 bytes each. At step S2220, an authentication step, an authentication process is performed between the components 510 and 520. When the authentication process at step S2100 fails, a series of Os is written in the NAND area 521 of the CF 520. When the authentication process is successful, at step S2230 the key Kcf, which is stored in the ROM 523 in the CF 520, is used to store the image generated by the digital camera 510 in the NAND area 521. The calculations, for which RC4 is used, are performed using 512 byte data strings, which were prepared at step S2210, the serial number of the CF 520 and the key Kcf stored in the CF 520, and the series that is obtained is written in the NAND area 521 of the CF 520. FIG. 35 is a flowchart for the authentication process performed between the components 520 and 530 at step S3000. At step S3100, an authentication step, the CF 520 and the CF driver 530 use the key Kpc to perform an authentication process and output the results. FIG. 36 is a detailed flowchart for the authentication process performed at step S3100 between the components 520 and 530. A data set pair consisting of the user ID and the key Kpc of the CF 520 are stored in advance in the key database 570. The user ID and the key Kpc are stored in the NAND area 521 of the CF 520. At step S3110 a random number is generated for the performance of the authentication process by the components 520 and 530, and a random number (a) is generated for use by the CF driver 530 during the authentication process. At step S3120, a series generation step, RC4 is used to calculate a series (b) that is output using the key Kpc, which is stored in advance in the NAND area 521 of the CF 520, and the random number (a), which is generated at step S3110. At step S3130, a generation step for a series to be used for an authentication process, the CF driver 530 uses RC4 to produce a series (c), which is output using the key Kpc and the random number (a). At step S3140, at which a series comparison is made as part of an authentication process for the components 520 and 530, the CF driver 530 compares the series (b) obtained at step S3120 with the series (c) obtained at step S3130. When the two series correspond, a result message, "The authentication process performed between the CF 520 and the CF driver 530 was successful," is output. When the two series differ, a result message, "The authentication process performed between the CF 520 and the CF driver 530 was not successful," is output. Preferably, when the authentication process fails, the following authentication process is not performed, and a warning message, "Since the authentication process performed between a compact flash driver and a compact flash failed, the validity of this image can not be confirmed," appears on the screen when the image held by the CF 520 is displayed on the display device 100. FIG. 37 is a flowchart for the authentication process performed between the components 530 and 540 at step S4000. At step S4100 the authentication process is performed by the components 530 and 540. The CF driver 530 and the JPEG image registration/storage application 540 use the key Kapp to perform the authentication process and output the result. FIG. 40 is a detailed flowchart for the authentication process performed at step 54110 between the components 530 and 540. At step S4100 a random number (a) is generated used by the application 540 for the authentication process. At step S4120 a series (b) is generated by the CF driver 530. The CF driver 530 uses RC4 to calculate the series (b), and uses the key Kapp to output it and the random number (a) obtained at step S4110. At step S4130 a series (c) is generated by the application 540. The application 540 uses RC4 to calculate the series (c), and uses the key Kapp and the random number (a) generated at step S4110 to output it. At step S4140, at which a comparison is made of the series used for the authentication process between the components 530 and 540, the series (b), calculated at step S4120, is compared with the series (c), calculated at step S4130. When the two series correspond, a result message, "The authentication process performed between CF driver 530 and the application 540 was successful," is output. When the two series differ, a result message, "The authentication process performed between the CF driver 530 and the application 540 was not successful," is output. Preferably, when the authentication process fails, the following authentication is not performed, and a warning message, "Since the authentication process performed between an application and a compact flash driver failed, the validity of this image can not be confirmed," appears on the screen when the image held by the CF 520 is displayed on the display device 100. When an image selected by a user for registration in the database is an image for which the validity could not be confirmed, a remark, "an image for which the validity could not be confirmed before registration" (i.e., the location of the image could not be confirmed), is included in the information that is to be embedded as an electronic watermark in the image. FIG. 38 is a flowchart for the ID embedding process performed at step S5000. At step S5200 a JPEG examination is performed in the CF 520. The examination is performed to determine whether the JPEG image stored in the CF 520 was altered. At step S5200, an ID embedding step, a data embedding/extraction key (Kdh) is used to embed, as an electronic watermark, an image ID (ID information) in the JPEG image. FIG. 39 is a detailed flowchart for the JPEG examination performed for the CF 520 at step S5100. At step S5110 a JPEG image division is performed for the CF 520; the JPEG image stored in the CF 520 is divided into strings of 512 bytes each. At step S5120, a step for the generation of a series used for data determination, the application 540 uses RC4 to produce a series (a), for which the 512-byte data strings obtained at step S5110, the serial number stored in the NAND area 521 of the CF 520, and the key Kcf stored in the ROM 523 of the CF 520 are used, and outputs the series. At step S5130, a step at which a series used for data determination is read, a series (b), stored in the NAND area 521 of the CF 520, is read and output. At step S5140, a step at which a comparison is performed for the series used for data determination, the series (a), produced at step S5120, is compared with the series (b), output at step S5130. If the two series correspond, the results message, "512 bytes of the data were altered," is output, and the next string of data is processed. If the two series differ, the result message, "Since 512 bytes of the data were altered, the pertinent JPEG data were altered," is output. FIG. 41 is a detailed flowchart for the ID embedding process performed at step S5200. At step S5210, a step for the generation of an image ID, data (an image ID) to be embedded as an electronic watermark in the JPEG image are generated. The image ID is a series generated using the authentication process history information obtained at steps S3100, S4100 and S5100, the photograph acquisition date, the photographer (a user ID), the registration date, and the photographic device (a digital camera ID). The authentication process history information represents the history of the authentication processes performed in the past, and includes information as to whether the authentication processes performed by the components, beginning with the digital camera 510 and ending with the application 540, were all successful, and information as to whether the JPEG image stored in the CF 520 was altered. When the authentication process history information is extracted, a process at which the authentication process failed (a process at which it was found an alteration was performed) is identified. At step S5220, an image ID embedding step, the data embedding/extraction key (Kdh) is used to embed the image ID, as an electronic watermark, in the JPEG image, and the obtained JPEG image is output. FIG. 42 is a detailed flowchart for the ID extraction/detection process performed at step S6000. At step S6100, an ID extraction step, the data embedding/extraction key (Kdh) is used- to extract the image ID from the JPEG image. At step S6200, a display step for the extraction/detection results, the ID, the results of the alteration examination, and an altered portion (if one is found) are displayed with the JPEG image. FIG. 43 is a detailed flowchart for the ID extraction process performed at step S6100. At step S6110, an image ID extraction step, the data (the image ID) embedded, as an electronic watermark, in the JPEG image are extracted using the data embedding/extraction key (kdh). At step S6120, a step for the analyzation of the image ID and for the alteration determination, the authentication process history information, the acquisition date, the photographer, the registration date and the photographic device are obtained from the results provided at step S6110, and, in addition, the electronic watermark is used to determine whether the image contains an altered portion. If an altered portion is found, program control moves to step S6130 to identify the altered portion. If no altered portion is found, the results (the authentication process history information, the acquisition date, the photographer, the registration date and the photographic device) are output. At step S6130, a step for identifying an altered portion, if an altered portion was found at step S6120, that portion is identified and changed into a binary image. The obtained binary image is then output with the results obtained at step S6120 (the authentication process history information, the acquisition date, the photographer, the registration date and the photographic device). Insurance Operation FIG. 44 is a outline diagram of a claim service and a damage assessment operation that use the data judging apparatus of the present invention. The present invention can be applied for a damage assessment operation whereby, when the property of an insured person is damaged and a contractor requests that under the terms of a non-life insurance policy an insurance company pay for the property damage, the insurance company conducts a damage assessment investigation, and based on the investigation, prepares and pays a specified amount. When the data judging apparatus of the present invention is used, a digital photograph obtained as evidence, to substantiate a property damage assessment, can be prevented from being altered or substituted, and the damage assessment operation can be performed safely and efficiently. In addition, its use for damage assessment purposes, the present invention can also be applied for various other operations, such as when photographs to be used as evidence are taken of objects and construction in process at civil engineering and construction sites, or when photographs are taken to be used for official real estate management, for environmental development and safety projects, and for disaster countermeasure planning. The outline of the damage assessment operation in FIG. 44 will not be explained by using automobile insurance as an example. When an insurance company 660 receives a report of an automobile accident from an insured client or from his or her agency 640, the insurance company 660 immediately notifies an insurance branch office 650 to assume responsibility for the processing required for the accident. Then, to perform the damage investigation, the branch manager assigns an assessor 630 who examines the damaged vehicle at a repair facility, uses a digital camera to take pictures of the damage for evidence, and prepares a damage assessment. Thereafter, the assessor 630 uses a PC to prepare a detailed assessment report to which, as evidence, a case photo file is attached. The assessor 630 then submits the assessment report to the branch manager for approval, and also registers the report in an accident case database 600. Subsequently, the branch manager evaluates and approves the case submitted by the assessor 630, and pays the assessed damage amount. Insurance Operation Process The damage assessment process using the method of the present invention is shown in FIG. 45. First, a photograph taken by the assessor 630 with the digital camera 510 is changed into a JPEG image in the digital camera 510. The JPEG image is then authenticated by the digital camera 510 and the compact flash 520, and is stored. Later, the assessor 630 selects, from a list, all the JPEG images stored in the CF 520 that are to be used as evidence, and registers the photographs using the damage assessment application 540. When the JPEG image list is displayed, an authentication process is performed by the CF 520 and the CF driver 530 and by the CF driver 530 and the damage assessment application 540. In addition, whether all the JPEG images stored in the CF 520 were input legally is determined by the authentication process performed by the digital camera 510 and the CF 520, and the results are displayed. The assessor 630 then refers to the results and selects a photograph to be registered as evidence in the accident case. Therefore, it can be confirmed that a JPEG image is valid. If the results of an authentication process are not obtained or the authentication process fails for a specific photograph, it may be possible that another photograph image altered by the PC was written in the CF 520. Thus, so long as this photograph will not be used for the following operation, an illegal activity can be prevented. The JPEG photograph selected by the assessor 630 is stored in the accident case database 600, and at this time, an alteration detection mark, used as an electronic watermark, and an image ID, which is formed using the acquisition date, the registration date, the photographer, the authentication process history information and the device used, are embedded in the JPEG image data. Then, when the insurance company manager evaluates the JPEG photograph stored in the damage assessment application 540, the alteration of the JPEG photograph is detected using the electronic watermark, and the image ID is extracted. The results are then displayed by the damage assessment application 540, and if the JPEG photograph was altered after it was registered, the altered portion is also displayed. The PC for detecting the alteration may be the same as the data embedding PC, or may be a remote PC 610 connected by a communication line. The present invention can be easily applied for an identification system. FIG. 47 is a diagram showing a smart card for which the present invention is used. The name and the ID number of the owner are recorded on the surface of a smart card 700. Preferably, a photographic image of the owner is printed. The features of a smart card 700 are that data for identifying an owner are embedded as an electronic watermark in the memory area on the smart card 700, and that, since the alteration detection data of this invention for specifying an altered portion are used as the electronic watermark, an alteration or an altered portion can be detected and identified. According to the identification data detection method, a smart card 700 is read by a smart card reader 710 to obtain identification data for an owner in which alteration detection data are embedded. The extracted alteration detection data are used to determine whether the identification data were altered, and when the identification data were altered, the altered portion is identified. The identification data are personal bibliographical data and biological characteristic data. Electronic data, such as a fingerprint, a voiceprint, an iris or a retina scan, are stored on the smart card 700 as an electronic watermark, which includes the alteration detection data of the present invention. The smart card reader 710 reads the electronic data to detect an alteration, and when an alteration is found, the altered portion is identified. Preferably, if no alteration is found, the information read by the smart card reader 710 is compared with information entered by a customer at a counter, and thereafter, the identification process is completed. Modifications of Content Data Judging Apparatus Other modifications of the data judging apparatus of the present invention will now be described. FIG. 27 is a diagram showing a simpler data judging apparatus than that in FIG. 26 (a digital camera 510 is connected to the PC as an accessory). A registration application 540 embeds a JPEG ID (electronic watermark) in a JPEG image using a key (Kdh), and stores the resultant JPEG image on a hard disk. A display application 550 extracts the ID from the JPEG image, determines whether the JPEG image was altered, and displays the results of the detection. If an altered portion is found, the altered portion is identified and displayed. FIG. 28 is a diagram showing an example for embedding an electronic watermark in the digital camera 510 in FIG. 26. A JPEG ID (electronic watermark) is embedded in a JPEG image acquired by the digital camera 510 using a key (Kdh). The JPEG image, which is stored in a storage medium 520, is then transmitted via a driver 530, and at a PC is stored on a hard disk by a registration application 540. A display application 550 extracts the ID from the JPEG image, determines whether the JPEG image was altered, and displays the results. If an alteration is found, an altered portion is identified and displayed. While the authentication process and the electronic watermark are protected by the above mentioned key, secrecy can be improved if tamper proof components are used. FIG. 29 is a diagram showing an example where the digital camera 510 in FIG. 26 is connected directly to a PC by a cable. A JPEG image acquired by the digital camera 510 is protected by authentication processes performed by components 510 and 530 using the key (Kpc), and by components 530 and 540 using the key (Kapp). A registration application 540 embeds a JPEG ID (electronic watermark) in the JPEG image using the key (Kdh), and stores the obtained JPEG image on the hard disk. A display application 550 extracts the ID from the JPEG image, performs an alteration determination, a nd displays the results. If an alteration is found, an altered portion is identified and displayed. While the authentication process and the electronic watermark are protected by the mentioned above keys, secrecy can be improved if | ||||||