JP2001078070A - Digital camera and picture alteration detection system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a digital camera which outputs picture data which enables a user to confirm whether picture data at the time of photographing has been altered or not. SOLUTION: An electric signal outputted from a CCD is converted to a digital signal in a step S101. In a step S103, digital data outputted from an A/D converter is recorded in a RAM. In a step S104, data recorded in the RAM is subjected to various kinds of picture correction. In steps S105 to S110, data corrected in the step S104 is compressed by the JPEG system. A feature data embedding position is determined in a step S106, and feature data is generated from picture data in a step S107. In a step S108, feature data is enciphered into encryption data. In a step S109, the enciphered feature data is embedded in the picture data.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital camera for recording a photographed image as digital data and a system for detecting alteration of image data recorded by the digital camera.

[0002]

2. Description of the Related Art Conventionally, when a photograph is taken, a camera is used in which light taken in from a lens is irradiated onto a film and a chemical reaction occurs to record an image. With the above camera, a photograph can be printed by developing the film and printing it on photographic paper. Since the reaction of silver chloride is generally used as the above chemical reaction, a photograph taken by such a camera is called a silver halide photograph.

On the other hand, in recent years, digital cameras that convert light into an electric signal by an optical sensor such as a CCD, convert the light into a digital signal, and then record the digital signal on a recording medium such as a flash memory have become widespread. With a digital camera,
Images can be easily stored and various processes can be easily performed by an individual using a processing device such as a personal computer, and a photograph can be printed without developing the film by outputting it with a printer. 2. Description of the Related Art Improvements in the printing quality of printers have made it possible to print high-quality photographs that are almost indistinguishable from silver halide photographs.

[0004]

However, when a photograph taken by a digital camera is used as an important proof photograph, such as when the photograph is to be used for a proof photograph such as non-life insurance, the image photographed by the digital camera becomes a personal computer. Etc., which makes it easier to process without leaving any trace of processing compared to silver halide photographs, making it difficult to discriminate even if a fraudulently tampered photograph is used. And there is a problem that it can be abused.

Accordingly, it is an object of the present invention to provide a digital camera which outputs image data capable of detecting whether or not the image data has been tampered with at the time of photographing, and an image tampering detection system using the same.

[0006]

According to the first aspect of the present invention, there is provided a digital camera, comprising: means for performing image processing on image data; and means for generating first characteristic data from image data after image processing. And means for embedding the first feature data in the image data, and a recording medium for recording the image data in which the first feature data is embedded. Therefore, after all image processing performed in the digital camera is completed, the first
Are embedded in the image data. Therefore, if the image data recorded on the recording medium at the time of photographing by the digital camera is changed even by one bit, the image data and the first feature data become inconsistent or the feature data is destroyed. Therefore, it can be determined that the image data has been tampered with after photographing. Also,
If the consistency between the image data and the first feature data is ensured, it can be determined that the image is as it was at the time of shooting. As a method of generating the first feature data, a method of obtaining a checksum of image data or a CRC (Cyclic Red
undancy check), a method for detecting an error in data communication, a hash value calculated by a one-way hash function, or the like can be used.

According to the digital camera of the present invention, since the image data is compressed, the capacity of the image data can be reduced.

According to the digital camera of the third aspect of the present invention, the digital camera includes means for encrypting the first characteristic data. Therefore, it is possible to prevent the feature data from being rewritten according to the alteration of the image.

According to the digital camera of the fourth aspect of the present invention, a public key for decrypting the encrypted characteristic data is attached to the image data corresponding to the secret key obtained by encrypting the first characteristic data. I do. Therefore, it is possible to easily authenticate that the data has been encrypted with the secret key.

According to the image tampering detection system of the present invention, a means for inputting image data, a means for removing first characteristic data from the image data, and an image from which the first characteristic data is removed The apparatus includes means for generating second characteristic data from the data, and means for comparing the first characteristic data with the second characteristic data. Therefore, if the first feature data and the second feature data match, it can be detected that the input image data has not been changed after being recorded by the digital camera.

According to the image tampering detection system of the present invention, when a public key is not attached to image data, it can be determined that there is a possibility of tampering. According to the image tampering detection system of the present invention, it is determined that there is a possibility of tampering when the additional information of the image data is different from that specific to the digital camera according to the first to fourth embodiments. I do. Therefore, when image data is captured by a specific digital camera, the possibility of tampering can be easily determined.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 2 is a block diagram for explaining the digital camera 1 according to the embodiment of the present invention. Control unit 11, condenser lens 12, CCD as optical sensor
(Charge Coupled Device) 13, A / D converter 14,
RAM (Random Access Memory) 15, flash memory 16 as an image recording medium for recording image data, interface 17 for inputting / outputting the contents of flash memory 16 to / from external personal computer 20, liquid crystal display capable of displaying images (LCD) 19 and the like. The control unit 11 includes a CPU and a ROM in which programs for performing various controls of the digital camera 1 are recorded.
And input / output means. The flash memory 16 may be built in the digital camera 1, may be a memory card detachable from the digital camera 1, or may include both of them.

FIG. 1 is a flow chart showing a process of taking a picture by the digital camera 1. When the user presses the shutter of the digital camera 1, step S101
Then, the light condensed by the condenser lens 12 is input to the CCD 13 and converted into an electric signal. The aperture and shutter speed of the condenser lens 12, that is, the accumulation time of the CCD 13 are controlled by the control unit 11 automatically or by a user's instruction. As the CCD 13, for example, R
(Red), G (Green), B (Blue) CCD1 in which a plurality of pixels having primary color filters are arranged in a matrix
3, a color image can be taken. C (Cyan), M (Magenta), Y (Yellow), G
In some cases, a CCD having a (Green) complementary color filter is used.

In step S102, the electric signal output from the CCD 13 is converted into a digital signal by the A / D converter 14. In step S103, the electric signal is converted into a digital signal.
Digital data output from DMA for high speed
(Direct Memory Access) and directly specifies the address of the RAM 15 without the intervention of the control unit 11 and is recorded. RA
DRAM with self-refresh function as M15
Can be used.

In step S104, various image corrections such as white balance adjustment, interpolation processing, and color correction are performed on the data recorded in the RAM 15. Here, other image processing such as enlargement / reduction of an image may be performed.

In steps S105 to S110, steps S104 and S104 are performed to increase the number of images to be recorded on the image recording medium.
Data corrected by JPEG (Joint Photographic E
xperts Group) to generate small-capacity image data. The JPEG compression is performed by the control unit 11 using software, and a dedicated circuit can be used for speeding up.

The JPEG compression procedure will be described below. In step S105, first, the image data is set to 8 × 8 pixels by 1
Divide into multiple blocks as a unit. For example, 640
80 × 60 = 48 for image data of × 480 pixels
It is divided into 00 blocks, and the processing is performed in block units.

Next, the relative relationship (spatial frequency) between the densities of the pixels is checked for each block of B1 to B480, and the DC
Each block is divided into a low-frequency term DCT0 to a high-frequency term DCT63 by a T (spread cosine transform) method. DCT0 to DCT63 are 8-bit values. FIG. 3 shows the DCT 63 of the high frequency term in hexadecimal. Then, quantization is performed using a predetermined quantization table so that many of the high-frequency terms become zero, and the compression ratio becomes high when Huffman coding is performed in a later process.

In step S106, the DCT 63, which is the highest frequency component of each block, is examined in order from the first block of the DCT-converted image data in order to determine the position where the feature data is to be embedded in the subsequent process. . Then, blocks whose DCT value is other than 0 and 1 are stored as embedded blocks. In the example shown in FIG. 3, B3, B4, B5, and B6 are selected and stored as embedded blocks. In this embodiment, since a 128-bit hash value is used, 1
28 blocks are selected. 128 embedded blocks
If the number of embedded blocks is less than the number of embedded blocks, when the number of missing embedded blocks matches the unexamined block, all remaining blocks are regarded as embedded blocks. Then, all the least significant bits of the DCT 63 of the embedded block are replaced with 0. Thereby, for example, the DCT 63 of the block B4 is F
Although rewritten from F to FE, small fluctuations at high frequencies are barely detectable to the naked eye, and image distortion is minimized.

In step S107, step S106
The control unit 11 generates feature data based on the image data partially rewritten in. As the feature data, for example, hash values calculated by various one-way hash functions can be used. In addition to a hash value, a known method such as a checksum or a CRC method that can detect whether or not data has been changed from the original can be applied to the present invention. By using these methods, different feature data can be assigned to each image data, and it is almost impossible to reproduce the original image data from the feature data. In this embodiment, a 128-bit hash value is calculated as the feature data. For example, an MD5, SHA or RIPEMD hash function can be used.

In step S108, the control unit 11 encrypts the characteristic data such as a hash value so that the characteristic data is not easily rewritten and converted into encrypted data. As an encryption method, a known method such as the RAS method using a public key and a secret key can be used. The encrypted data encrypted with the secret key can be decrypted using the public key paired with the secret key. The secret key is recorded in the digital camera 1 as a file with a hidden attribute. The secret key must not be known to others, and in this embodiment, the user does not need to know the secret key. In general, it is very difficult to find a corresponding private key from a public key. As a result, it is possible to prevent the image data from being changed to another image data that can obtain the same feature data, and from being rewritten in accordance with the change in the image data.

In step S109, the encrypted data obtained by encrypting the hash value is written one bit at a time to the least significant bit of the DCT 63 of the selected embedded block, thereby minimizing the deterioration of the image and reducing the characteristic data to the image data. Embed in In the case of a color image, JPEG image data is Y (luminance), U, V (hue).
, But the encrypted feature data is embedded in the Y component.

In step S110, the data in which the encrypted data is embedded is subjected to Huffman encoding to compress the data. In Huffman coding, the reversibility of data is satisfied, and there is no loss of data before and after processing. The compression ratio can be changed by changing the degree of quantization by the quantization table in S105.

In step S111, the image data compressed in S110 is recorded as a JPEG file 30 in the flash memory 16 as an image recording medium. The flash memory 16 is a rewritable recording medium capable of storing recorded contents without power supply, and is built in the digital camera 1 or is detachably attached to the digital camera 1. Generally JPEG file 3
0 is composed of a header section 31 including additional information such as a data length and a compression ratio, as shown in FIG. 4, and an image data section 32. In the case of a JPEG file 30 recorded by the digital camera 1, information such as a photographing date and photographing conditions may also be recorded in the header section 31. In this embodiment, the public key 33 corresponding to the secret key used for encryption is further added to the header section 31 and recorded.

In the above example, the feature data is embedded in the middle of the JPEG compression process. However, the image data is partially decoded after the normal JPEG compression is performed up to Huffman encoding without embedding the feature data. Then, the feature data may be embedded by the same process as steps S106 to S109, and Huffman coding may be performed again.

The digital camera 1 as described above, a computer such as a personal computer 20 having means for inputting image data output from the digital camera 1, and whether or not the image data recorded by the digital camera 1 has been changed The image tampering detection system is configured by a detection program installed in the personal computer 20 or the like to determine the falsification.

The process of detecting image tampering by the image tampering detection system of this embodiment will be described with reference to the flowchart shown in FIG. In step S201, image data is read from the digital camera into the personal computer 20 by the detection program. As means for reading image data into the personal computer 20, the personal computer 20 is connected to the interface 17 of the digital camera 1 via a serial cable 18 or the like,
When the EG file is transferred to the personal computer 20, or when the flash memory 16 is detachably formatted in a format compatible with the personal computer 20, the JPEG file recorded on the flash memory 16 via the adapter is used. It is also possible to read 30 directly by the personal computer 20.

In step S202, the read JP
By examining the header of the EG file, it is detected whether or not a public key is attached and whether or not additional information unique to the digital camera of this embodiment is recorded. If either one is not found, it is determined that the JPEG file has been created by a device other than the digital camera of the present embodiment, or that the image data may have been tampered with.

In step S203, the above-described step S
In the same procedure as when the block in which the feature data is embedded is selected in 106, a block in which the feature data is to be embedded is selected, and 128-bit encrypted data is extracted.

In step S204, "0" is written to all bits in which the encrypted data is embedded, and original image data before the encrypted data is embedded is generated. In step S205, 1
Calculate a 28-bit hash value.

In step S206, step S203
Using the public key written in the header of the JPEG file, it is confirmed that the encrypted data extracted by the above is encrypted by the secret key, and at the same time, the encryption is decrypted. Thereby, a hash value before encryption is obtained.

In step S207, step S205
The hash value calculated in step S206 is compared with the hash value calculated in step S206, and if they match, it is determined that the image data has not been altered after being photographed by the digital camera 1 of the present embodiment, If they do not match, it is determined that the image data has been altered from the time of shooting. Also, in step S206, even if the encrypted data cannot be decrypted with the public key, it is considered that the image data was not captured by the digital camera 1 of the embodiment of the present invention or changed after the capture.

Therefore, when using the image tampering detection system according to the embodiment of the present invention, the submitter of the photograph is required to output a file containing the image data which has been output from the digital camera 1 and has not been modified (in this embodiment, the JPEG file 30). ) Is recorded on a recording medium such as a floppy (registered trademark) or a flash memory 16 which is a detachable recording medium.
Is removed from the digital camera 1 and submitted together with the printed photo or at the request of the other party. The receiving side reads the received file using the detection program installed in the personal computer 20 and checks it, thereby confirming that the image data of the file has not been changed since the time when it was output from the digital camera 1. be able to.

By providing the detection program with a function of displaying an image of image data such as the JPEG file 30, it is possible to confirm that the printed picture and the displayed image are the same.

As described above with reference to the embodiments, by using the digital camera of the present invention and the image tampering detection system using the same, the photograph taken by the digital camera has not been changed since the photographing. Can be confirmed.

In the above embodiment, JPEG-compressed data is recorded on the image recording medium as image data. However, the present invention is not limited to data compressed by another compression method or uncompressed data recorded as image data. Can also be applied. Further, in the present embodiment, the feature data is encrypted and embedded in the image data portion of the JPEG file and recorded. However, according to the present invention, the feature data can be written in any position of the image data, such as writing in the header portion. Good.

[Brief description of the drawings]

FIG. 1 is a flowchart illustrating a procedure for recording an image by a digital camera according to an embodiment of the present invention.

FIG. 2 is a block diagram illustrating a digital camera according to an embodiment of the present invention.

FIG. 3 is a schematic diagram for explaining a method for calculating feature data of image data according to an embodiment of the present invention.

FIG. 4 is a schematic diagram for explaining a structure of a JPEG file according to an embodiment of the present invention.

FIG. 5 is a flowchart illustrating a procedure for detecting tampering of image data according to the embodiment of the present invention.

[Explanation of symbols]

 Reference Signs List 1 digital camera 11 control unit 12 condenser lens 13 CCD (imaging unit) 14 A / D conversion unit 15 RAM 16 flash memory 17 interface 18 connection cable 19 liquid crystal display unit (LCD) 20 personal computer 30 JPEG file 31 header unit 32 image Data 33 public key

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) H04N 5/765 H04N 5/781 510L 5C075 5/781 5/91 J 5C076 5/91 7/08 Z 5J104 7 / 08 7/133 Z 7/081 7/30 F term (reference) 5B057 AA11 BA24 BA29 CA01 CA19 CB19 CE08 CH11 DA08 DA16 DB06 DC32 5C022 AA13 AC31 AC42 AC54 AC69 5C053 FA08 FA14 GB23 GB36 KA04 KA24 KA25 LA01 LA11 5C059 KK43 MA MC11 ME02 PP01 PP15 RB08 RC35 SS15 UA02 UA05 5C063 AB03 AC02 AC10 CA09 CA11 DA07 DA13 DB09 5C075 CD05 EE03 5C076 AA14 BA02 BA03 CA08 5J104 AA08 AA14 LA03 NA02 NA15 NA27 PA14

Claims (7)

[Claims] An imaging unit configured to convert light from an imaging target into image data; a unit configured to perform image processing on the image data; a unit configured to generate first feature data from the image data after the image processing; A digital camera comprising: means for embedding the first feature data in the image data; and a recording medium for recording the image data in which the first feature data is embedded. 2. The digital camera according to claim 1, further comprising means for compressing the image data. 3. The digital camera according to claim 1, further comprising means for encrypting the first characteristic data. 4. The digital camera according to claim 3, further comprising: means for attaching a public key corresponding to a secret key for encrypting the first characteristic data to the image data. 5. An image tampering detection system using the digital camera according to claim 1, wherein said image data is input, and said first feature data is obtained from said image data. Means for removing the second feature from the image data from which the first feature data has been removed.
An image tampering detection system comprising: means for generating feature data; and means for comparing the first feature data and the second feature data. 6. An image tampering detection system using a digital camera according to claim 4, wherein: a means for inputting the image data; a means for removing the first feature data from the image data; From the image data from which the feature data of
Means for generating the characteristic data of the above, means for comparing the first characteristic data with the second characteristic data, and means for determining that there is a possibility of tampering when the public key is not attached to the image data An image tampering detection system comprising: 7. The apparatus according to claim 5, further comprising: means for determining that there is a possibility of tampering when the additional information of the image data is different from information unique to the digital camera. Image tampering detection system.