Abstract:
In an image authentication system, a printing unit prepares a code in a form of an image of a different density in any two adjacent blocks, and prints the code onto a recording medium as a printed image. A storage unit stores therein image data corresponding to printed images and codes to be embedded in image data corresponding to the printed images in a correlated manner. An authenticating unit receives scanned image data corresponding to a printed image, extracts a code embedded in the scanned image data and authenticates the printed image corresponding to the scanned image data based on extracted code.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention generally relates to a technology for authenticating images printed on a recording medium and specifically relates to authenticating the images based on codes embedded in the images.  
         [0003]     2. Description of the Related Art  
         [0004]     The technology of embedding a code in an image and decoding the code to perform authentication has been known in the art. For example, an image processing apparatus disclosed in Japanese Patent Laid-Open Publication No. 2005-276561 describes a decoding process of an image printed or imprinted on a recording medium (hereinafter, “printed document”), after the code has been embedded into the image by the conventional code embedding technology, in which the image is output to a printed document or to a display device and then decoded upon receiving an image of the printed document from an input device such as a camera. The decoding process involves decoding the original code by the difference in the average densities of the adjoining blocks of the input image.  
         [0005]     The conventional image processing apparatus described above performs authentication of the contents of the printed document in the following manner. If a receipt (as shown in  FIG. 13 ) is presented as a document to be authenticated, the image processing apparatus embeds the data to be authenticated (for example, as shown in  FIG. 13 , data such as Employee Code and Serial No. for identifying a concerned person) as a code (for example, a steganographic identification (ID) shown in  FIG. 13 ) into an image (for example, “ABC” shown in  FIG. 13 ) imprinted in the receipt, and outputs the receipt along with the image imprinted in the receipt to a printed document. The image processing apparatus then decodes the image of the printed document, restores the steganographic ID, and authenticates the printed document based on the restored contents of steganographic ID.  
         [0006]     For example, the image “ABC” imprinted in the receipt has the Employee Code 12345678 and the Serial No. 1234 embedded into it. An image of the entire receipt including the image ABC is output to a printed document. The image imprinted in the printed document is decoded to restore the steganographic ID into Employee Code and Serial No., and the printed document is authenticated based on the Employee Code and Serial No.  
         [0007]     However, the disadvantage of the conventional technology is that only limited amount of data can be embedded in the code, enabling the image of the printed document to be authenticated if less content is involved, but not if the content involved is large. That is, in the example presented above, the Employee Code and the Serial No. can be embedded as a steganographic ID. However, the employee or company name and the amount cannot be embedded, and hence the contents of the receipt cannot be authenticated.  
       SUMMARY OF THE INVENTION  
       [0008]     It is an object of the present invention to at least partially solve the problems in the conventional technology.  
         [0009]     According to an aspect of the present invention, an image authentication system includes a printing unit that prepares a code in a form of an image of a different density in any two adjacent blocks, and prints the code onto a recording medium as a printed image; a storage unit that stores therein image data corresponding to printed images and codes to be embedded in image data corresponding to the printed images in a correlated manner; and an authenticating unit that receives scanned image data corresponding to a printed image, extracts a code embedded in the scanned image data and authenticates the printed image corresponding to the scanned image data based on extracted code.  
         [0010]     According to another aspect of the present invention, a printed image is printed by the printing unit of the above image authentication system.  
         [0011]     According to still another aspect of the present invention, an image authentication method includes preparing a code in a form of an image of a different density in any two adjacent blocks; printing prepared code onto a recording medium as a printed image; storing image data corresponding to printed images and codes to be embedded in image data corresponding to the printed images in a correlated manner in a storage unit; and receiving scanned image data corresponding to a printed image; extracting a code embedded in the scanned image data; and authenticating the printed image corresponding to the scanned image data based on extracted code.  
         [0012]     According to still another aspect of the present invention, a computer-readable recording medium stores therein a computer program that causes a computer to implement the above image authentication method.  
         [0013]     The above and other objects, features, advantages and technical and industrial significance of this invention will be better understood by reading the following detailed description of presently preferred embodiments of the invention, when considered in connection with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0014]      FIG. 1  is a schematic for explaining an encoding process according to a first embodiment of the present invention;  
         [0015]      FIG. 2  is an image with a code embedded therein;  
         [0016]      FIG. 3  is a schematic for explaining the overview and a characteristic feature of an image authentication system according to the first embodiment;  
         [0017]      FIG. 4  is a schematic for explaining an authentication process performed by the image authentication system according to the first embodiment;  
         [0018]      FIG. 5  is a block diagram of an image processing apparatus according to the first embodiment;  
         [0019]      FIG. 6  is an original image data;  
         [0020]      FIG. 7  is a schematic for explaining an image data having a steganographic ID is embedded therein;  
         [0021]      FIG. 8  is a block diagram of a steganographic-ID management server according to the first embodiment;  
         [0022]      FIG. 9  is a block diagram of a scanner according to the first embodiment;  
         [0023]      FIG. 10  is a flowchart of the process performed by the image authentication system according to the first embodiment;  
         [0024]      FIG. 11  is a schematic for explaining an image authentication system according to a second embodiment of the present invention;  
         [0025]      FIG. 12  is a schematic of a computer that implements the methods according to the first and the second embodiments; and  
         [0026]      FIG. 13  is a schematic for explaining a conventional image authentication process. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]     Exemplary embodiments of the present invention are explained next with reference to the accompanying drawings.  
         [0028]     Important terms used in a first embodiment are explained first, followed by an overview and characteristic feature of the image authentication system according to the first embodiment, a configuration of an image processing apparatus, a steganographic ID managing server, a process flow of an image authentication process, and finally the effects due to the first embodiment.  
         [0029]     The term Steganographic ID used below refers to an image of a different density in the form of a code, and which is imperceptible to the human eye, embedded between adjoining blocks.  
         [0030]     A process performed by an image processing apparatus  10 ″ according to an embodiment of the present invention when embedding a steganographic ID in image data is explained next with reference to  FIG. 1  and  FIG. 2 .  FIG. 1  is a schematic of the encoding process.  FIG. 2  is a drawing of an image in which a code has been embedded.  
         [0031]     As shown in  FIG. 1 , the encoding process performed by the image processing apparatus  10  includes setting a code, for example, a 16-bit code “1010110101001010”, to be embedded into an original image (code setting step), dividing the original image data into blocks of M rows×N columns, and outputting the resultant data as image data after division (block dividing step). In the next step, the image processing apparatus  10  regards two adjacent blocks of the image data after division as a pair and extracts a density distribution of each block as block density data (block extraction step).  
         [0032]     An image processing apparatus  10  then determines an average density of each block based on the block density data (averaging step shown). Next, the image processing apparatus  10  compares a magnitude relation of characteristic amount (for example, the average densities, granularity, chroma, density concentration or dispersion) of the blocks regarded as a pair (comparison step).  
         [0033]     Next, the image processing apparatus  10  performs a process of embedding a code C in the image data after division based on the result of comparison done at the previous comparison step (encoding step). Specifically, the image processing apparatus  10  determines whether the magnitude relation of the each pair of blocks coincides with the code to be embedded, and if the magnitude relation of the pair of blocks coincides with the code, maintains the magnitude relation of the characteristic amount.  
         [0034]     On the other hand, if the magnitude relation of the pair of blocks does not coincide with the code, the image processing apparatus recalculates the characteristic amount of the block having a smaller characteristic amount of the pair of blocks by adding a predetermined amount to its average value while recalculating the characteristic amount of the block having a larger characteristic amount of the pair of block by subtracting the predetermined amount from its average value, and outputs an image data with recalculated characteristic amounts of the two blocks regarded as a pair.  
         [0035]     The encoding process is explained in greater detail with reference to  FIG. 2 . After setting a code to be embedded in the original image, the original image data is divided into the image data after division having M rows×N columns (16×16 in the example shown in  FIG. 2 ). An image data after division I 1  shown in  FIG. 2  includes 256 blocks (16×16 shown in  FIG. 2 ), having blocks B 111 , Br 11 , B 118 , Br 18 , B 121 , Br 21 , B 1168 , B 4168 . One block is of 64×64 pixels. The original image data is formed in a predetermined format (Joint Photographic Experts Group (JPEG), Graphics Interchange Format (GIF), etc.)  
         [0036]     Next, the image processing apparatus  10  regards two adjoining blocks as a pair (for example, block B 111  and block Br 11 ), and extracts density distribution of the pair of blocks B 111  and Br 11  as block density data.  
         [0037]     The image processing apparatus  10  then determines the left side average density data corresponding to the block B 111  and the right side average density data corresponding to the block Br 11  from the block density data. The image processing apparatus then compares n-th bit (where n=1, 2, , 16) from the leftmost bit shown in  FIG. 2 ) of the code with the bit determination result determined from the magnitude relation of the left side average density data and the right side average density data, and performs the process of embedding the code in the image data after division (original image data) based on the comparison result.  
         [0038]     The overview and the characteristic feature of the image authentication system according to the first embodiment are explained with reference to  FIG. 3  and  FIG. 4 .  FIG. 3  is a schematic for explaining the overview and the characteristic feature of the image authentication system according to the first embodiment.  FIG. 4  is a schematic for explaining an authentication process performed by the image authentication system according to the first embodiment.  
         [0039]     An overview of authentication of an image embedded in a printed document is presented in the image authentication system according to the first embodiment. The main characteristic feature of the image authentication system according to the first embodiment is that authentication of the image imprinted in the printed document can be carried out regardless of the image content in the printed document.  
         [0040]     The main characteristic feature of the image authentication system according to the first embodiment is explained next. An image authentication system  1  according to first embodiment includes the image processing apparatus  10 , a steganographic-ID management server  20  and a scanner  30 . The image processing apparatus  10  embeds a steganographic ID (see ( 1 ) of  FIG. 3 ) in the image (the image embedded in the receipt, shown in  FIG. 3 ) by the encoding process described above, and outputs the image data on a printed document (see ( 2 ) of  FIG. 3 ). Specifically, the image processing apparatus  10  embeds data identifying a concerned person (Employee Code 12345678 and Serial No 1234 shown in  FIG. 3 ) as steganographic ID into the image (the image imprinted in the receipt in  FIG. 3 ) data and outputs the image to a printed document. After the details have been filled in by hand in the receipt (see ( 3 ) of  FIG. 3 ), and receipt with the handwritten data is presented to the image processing apparatus  10  once again, the image processing apparatus  10  reads the entire image including the handwritten section, and forwards it to the steganographic-ID management server  20  with a request to register the image of the printed document.  
         [0041]     Upon receiving the request, the steganographic-ID management server  20  extracts the steganographic ID from the image of the printed document, and registers the steganographic ID and the image of the entire printed document in a correlated form in a steganographic-ID management table  23   a  (see ( 4 ) of  FIG. 3 ). The scanner  30  receives the actual printed document, scans the image data of the actual printed document, extracts the steganographic ID (“123456781234” in  FIG. 4 ) from the image portion with the steganographic ID embedded therein (see ( 5 ) of  FIG. 3 ), and forwards the extracted steganographic ID to the steganographic-ID management server  20 . The steganographic-ID management server  20  reads from the steganographic-ID management table  23   a  the image data of the printed document corresponding to the steganographic ID received from the scanner  30  and authenticates the image data by cross-checking it against the image data of the printed document read from the steganographic-ID management table  23   a  (see ( 6 ) of  FIG. 3 ).  
         [0042]     The processes ( 5 ) and ( 6 ) in  FIG. 3  are explained in further detail with reference to  FIG. 4 . After reading the image data from the printed document (the actual receipt in  FIG. 4 ), the scanner  30  extracts the steganographic ID (“123456781234” in  FIG. 4 ) from the image data of the actual printed document, and forwards the steganographic ID to the steganographic-ID management server  20  (see ( 1 ) of  FIG. 4 ). Upon receiving the steganographic ID, the steganographic-ID management server  20  reads the image data of the printed document corresponding to the steganographic ID from the steganographic-ID management table  23   a , and forwards the image data of the printed document to the scanner  30  (see ( 2 ) of  FIG. 4 ). The scanner  30  receives and displays the image data of the printed document so that the actual printed document and the image data of the printed document can be visually compared to determine whether they match (see ( 3 ) of  FIG. 4 ). If the actual printed document and the image data of the printed document match, the actual receipt is authenticated as being genuine. Otherwise, the actual receipt is regarded as a counterfeit (see ( 4 ) of  FIG. 4 ).  
         [0043]     Thus, in the image authentication system  1 , the printed document is output with an image of a different density in the form of a steganographic ID is embedded between adjoining blocks. The steganographic ID embedded in the image imprinted in the printed document and the image of the printed document are registered in a correlated form. The image imprinted in the printed document is authenticated by extracting the steganographic ID embedded in the image. Consequently, the image imprinted in the printed document can be authenticated regardless of the image content in the printed document.  
         [0044]     The configuration of the image processing apparatus  10  is explained next with reference to  FIG. 5 .  FIG. 5  is a block diagram of the image processing apparatus  10 . The image processing apparatus  10  includes a communication control I/F  11 , an input/output control I/F  12 , an input unit  13 , an output unit  14 , a controller  15 , and a storage unit  16 . The image processing apparatus  10  is connected to the steganographic-ID management server  20  and the scanner  30  via a network  40 . The function of each part of the image processing apparatus  10  is explained next.  
         [0045]     The communication control I/F  11  controls the communication related to exchange of various types of data between the image processing apparatus  10  and the steganographic-ID management server  20 . Specifically, the communication control I/F  11  forwards the contents of the printed document to the steganographic-ID management server  
         [0046]     The input/output control I/F  12  controls the data transfer between the input unit  13  and the output unit  14 , the controller  15 , and the storage unit  16 .  
         [0047]     The input unit  13  inputs the original image data, the steganographic ID, and the image of the printed document. Specifically, the input unit  13  inputs the original image data formed in a predetermined format (such as Joint Photographic Experts Group (JPEG), Graphics Interchange Format (GIF), etc.) by a scanner, a storage medium or communication, the steganographic ID composed of 16 bits, such as “1010110101001010” by a keyboard, and the image of the printed document by the scanner, the storage medium or communication, after details (such as “Company name” and “Amount” shown in  FIG. 3 ) have been filled in by hand in the printed document output by a printed-document output unit  15   b . The printed-document output unit  15   b  is described in a later section.  
         [0048]     The output unit  14  outputs the image data having information (such as the steganographic ID) embedded therein to the printed document. That is, the output unit  14  outputs the image data encoded with the 16-bit steganographic ID “1010110101001010” stored in an encoded-image-data storage unit  16   c  to the printed document. The encoded-image-data storage unit  16   c  is explained in a later section.  
         [0049]     The storage unit  16  contains data and computer programs required by the controller  15  for various processes. The storage unit  16  includes an original-image-data storage unit  16   a , a steganographic-ID storage unit  16   b , the encoded-image-data storage unit  16   c , and a printed-document-image storage unit  16   d.    
         [0050]     The original-image-data storage unit  16   a  stores therein the original image data in which a code is to embedded by the image processing apparatus  10 . Specifically, the original-image-data storage unit  16   a  the original image data shown in  FIG. 6 , formed in a predetermined format (such as Joint Photographic Experts Group (JPEG), Graphics Interchange Format (GIF), etc.).  
         [0051]     The steganographic-ID storage unit  16   b  stores therein the steganographic ID to be embedded into the original image data. For example, the steganographic-ID storage unit  16   b  stores therein the Employee Code (for example, “12345678” shown in  FIG. 3 ) assigned to each employee, and the Serial No. (“1234” shown in  FIG. 3 ), which increments with every printed document output by the printed-document output unit  15   b  described later.  
         [0052]     The encoded-image-data storage unit  16   c  stores therein the image data with the steganographic ID embedded therein. In other words, the encoded-image-data storage unit  16   c  stores therein the image data after the steganographic ID is embedded into it by a steganographic-ID embedding unit  15   a  described later. Specifically, the encoded image data has embedded into it the 16-bit steganographic ID, such as “1010110101001010”, in a repeating manner, as shown in  FIG. 7 .  
         [0053]     The printed-document-image storage unit  16   d  stores therein the image of the printed document. That is, the printed-document-image storage unit  16   d  stores therein the image of the printed document after details (such as “Company name” and “Amount”) have been filled in by hand in the printed document output by the printed-document output unit  15   b.    
         [0054]     The controller  15  executes various processes and includes an internal memory for storing programs and necessary data required for regulating the various processes. In close relevance to the present invention, the controller  15  includes the steganographic-ID embedding unit  15   a , the printed-document output unit  15   b , and a registration-request forwarding unit  15   c . The printed-document output unit  15   b  substantially corresponds to an output unit in the claims.  
         [0055]     The steganographic-ID embedding unit  15   a  embeds the steganographic ID into the original image data. Specifically, the steganographic-ID embedding unit  15   a  converts the Employee Code and the Serial No. stored in the steganographic-ID storage unit  16   b ″ from a decimal number to a binary number and embeds the binary number as steganographic ID in the original image data stored in the original-image-data storage unit  16   a , and stores the encoded image data in the encoded-image-data storage unit  16   c.    
         [0056]     The printed-document output unit  15   b  outputs the encoded image data to the printed document. Specifically, the printed-document output unit  15   b  outputs the image data stored in the encoded-image-data storage unit  16   c  to the printed document.  
         [0057]     The registration-request forwarding unit  15   c  forwards a request to the steganographic-ID management server  20  to register the image of the printed document and the steganographic ID embedded in the image imprinted in the printed document in a correlated form. Specifically, the registration-request forwarding unit  15   c  reads and forwards the entire image including the handwritten section to the steganographic-ID management server  20  with the request for registration.  
         [0058]     The configuration of the steganographic-ID management server  20  is explained next with reference to  FIG. 8 .  FIG. 8  is a block diagram of the steganographic-ID management server  20 . The steganographic-ID management server  20  includes a communication control I/F  21 , a controller  22 , and a storage unit  23 . The steganographic-ID management server  20  is connected to the image processing apparatus  10  and the scanner  30  via the network  40 . The function of each part of the steganographic-ID management server  20  is explained next.  
         [0059]     The communication control I/F  21  controls communication related to the exchange of various types of data between the steganographic-ID management server  20  and the image processing apparatus  10  as well as the scanner  30 . Specifically, the communication control I/F  21  receives the contents of the printed document from the image processing apparatus  10  and steganographic ID from the scanner  30 .  
         [0060]     The storage unit  23  stores therein data and computer programs required by the controller  22  for various processes. The storage unit  23  includes the steganographic-ID management table  23   a.    
         [0061]     The steganographic-ID management table  23   a  stores therein the image of the printed document and the steganographic ID embedded in the image imprinted in the printed document in a correlated form. Specifically, the steganographic-ID management table  23   a  stores the image of the printed document received from the image processing apparatus  10  and the steganographic ID embedded in the image imprinted in the printed document.  
         [0062]     The controller  22  executes various processes and includes an internal memory for storing computer programs and necessary data required for regulating the various processes. The controller  22  includes a steganographic-ID extracting unit  22   a  a registering unit  22   b , and an image-data forwarding unit  22   c . The registering unit  22   b  substantially corresponds to a registering unit in the claims.  
         [0063]     The steganographic-ID extracting unit  22   a  extracts the steganographic ID embedded in the image. Specifically, the steganographic-ID extracting unit  22   a  extracts the steganographic ID embedded in the image of the printed document received from the image processing apparatus  10  and outputs the extracted steganographic ID to the registering unit  22   b.    
         [0064]     The registering unit  22   b  registers the image of the printed document and the steganographic ID imprinted in the image imprinted in the printed document in a correlated form. Specifically, the registering unit  22   b  registers the received image of the printed document and the steganographic ID extracted by the steganographic-ID extracting unit  22   a  from the steganographic-ID management table  23   a  in a correlated form.  
         [0065]     The image-data forwarding unit  22   c  forwards the image data to the scanner  30 . Specifically, after the steganographic ID is received, the image-data forwarding unit  22   c  reads the image data of the printed document corresponding to the steganographic ID from the steganographic-ID management table  23   a , and forwards the read image of the printed document to the scanner  30 .  
         [0066]     The configuration of the scanner  30  is explained next with reference to  FIG. 9 .  FIG. 9  is a block diagram of the scanner  30 . The scanner  30  includes a communication control I/F  31 , a controller  32 , an input unit  33 , and a monitor  34 , and is connected to the image processing apparatus  10  and the steganographic-ID management server  20  via the network  40 . The function of each part of the scanner  30  is explained next.  
         [0067]     The communication control I/F  31  controls communication related to the exchange of various types of data between the scanner  30  and the steganographic-ID management server  20 . Specifically, the communication control I/F  31  forwards the steganographic ID to the steganographic-ID management server  20  and receives the image data of the printed document from the steganographic-ID management server  20 .  
         [0068]     The input unit  33  inputs the printed document. Specifically, the input unit  33  receives and inputs the actual printed document and inputs into an image scanning unit  32   a  described later. The monitor  34  displays the image data. Specifically, the monitor  34  displays the image data forwarded by the steganographic-ID management server  20  and received by an image display unit  32   d  described later.  
         [0069]     The controller  32  executes various processes and includes an internal memory for storing programs and necessary data required for regulating the various processes. In close relevance to the present invention, the controller  32  includes the image scanning unit  32   a , a steganographic-ID extracting unit  32   b , a steganographic-ID forwarding unit  32   c , and the image display unit  32   d . The image display unit  32   d  substantially corresponds to an authenticating unit in the claims.  
         [0070]     The image scanning unit  32   a  reads the image data from the printed document. Specifically, the image scanning unit  32   a  reads image data from the printed document (for example, the actual receipt) input by the input unit  33 , and forwards the read image data to the steganographic-ID extracting unit  32   b.    
         [0071]     The steganographic-ID extracting unit  32   b  extracts the steganographic ID from the image data. Specifically, the steganographic-ID extracting unit  32   b  performs a decoding process on the image data received from the image scanning unit  32   a  to extract the steganographic ID, and outputs the extracted steganographic ID to the steganographic-ID forwarding unit  32   c.    
         [0072]     The steganographic-ID forwarding unit  32   c  forwards the steganographic ID to the steganographic-ID management server  20 . Specifically, the steganographic-ID forwarding unit  32   c  forwards the steganographic ID received from the steganographic-ID extracting unit  32   b  to the steganographic-ID management server  20 .  
         [0073]     The image display unit  32   d  displays the image data of the printed document. Specifically, the image display unit  32   d  displays the image data received from the steganographic-ID management server  20  on the monitor  34 , and enables the actual receipt and the image data of the printed document displayed on the monitor to be visually compared to determine whether they match. If the actual printed document and the image data of the printed document match, the actual receipt is authenticated as being genuine. Otherwise, the actual receipt is regarded as a counterfeit.  
         [0074]     The processes performed by each of the units of the image authentication system  1  are explained next with reference to  FIG. 10 .  FIG. 10  is a flowchart of the processes performed by each of the units of the image authentication system  1 .  
         [0075]     The image processing apparatus  10  of the image authentication system  1  converts the Employee Code and the Serial No. stored in the steganographic-ID storage unit  16   b  from decimal number to binary number and embeds the converted binary code in the original image data stored in the original-image-data storage unit  16   a  (step S 101 ), and outputs the encoded image data to the printed document (step S 102 ).  
         [0076]     Once other details in the receipt are filled in by hand and the receipt along with the handwritten section is presented again, the image processing apparatus  10  reads the image of the entire receipt including the handwritten section (step S 103 ), and forwards the entire image to the steganographic-ID management server  20  with a request for registration (step S 104 ).  
         [0077]     The steganographic-ID management server  20  extracts the steganographic ID embedded in the image of the printed document received from the image processing apparatus  10  (step S 105 ), and registers the extracted steganographic ID and the image of the received printed document in a correlated form (step S 106 ). The scanner  30  receives the actual printed document, scans the image data from the actual printed document (step S 107 ), extracts the steganographic ID embedded in the image section, and forwards the extracted steganographic ID to the steganographic-ID management server  20  with a request for authentication (step S 108 ).  
         [0078]     Upon receiving the steganographic ID, the steganographic-ID management server  20  reads the image data of the printed document corresponding to the received steganographic ID from the steganographic-ID management table  23   a , and forwards the read image of the printed document to the scanner  30  (step S 109 ).  
         [0079]     The scanner  30  displays the image data of the printed document received from the steganographic-ID management server  20  and enables image data of the printed document to be compared with the actual receipt. If the image imprinted in the actual receipt and the image data of the printed document match, the actual receipt is authenticated as genuine. Otherwise, the actual receipt is regarded as a counterfeit (step S 110 ).  
         [0080]     Thus, the printed document is output with an image of a different density in the form of a steganographic ID is embedded between adjoining blocks. The steganographic ID embedded in the image imprinted in the printed document and the image of the printed document are registered in a correlated form in the steganographic-ID management table  23   a . The image imprinted in the printed document is authenticated by extracting the steganographic ID embedded in the image. Consequently, the image imprinted in the printed document can be authenticated regardless of the image content in the printed document.  
         [0081]     Further, according to the first embodiment, the printed document is output with only the steganographic ID imprinted therein, and the printed document with the image containing the steganographic ID is received, and the image of the printed document and the steganographic ID are registered in the steganographic-ID management table  23   a  in a correlated form. Thus, the process of embedding the code in the image data during registration can be done away with.  
         [0082]     According to the first embodiment, the steganographic ID imprinted in the printed document is extracted, and the image in the steganographic-ID management table  23   a  corresponding to the extracted steganographic ID is displayed on the monitor  34 .  
         [0083]     The other embodiments of the present invention are described collectively as a second embodiment.  
         [0000]     (1) Registration  
         [0084]     In the first embodiment, the image data is output to a printed document followed by the registration of the contents of the printed document and steganographic ID in a correlated form. The registration of the image data that is output and the steganographic ID embedded in the image data can be registered in a correlated form at the same time the image data is output to a printed document.  
         [0085]     Specifically, as shown in  FIG. 11 , once the details (for example, “Company name”, and “Amount”) filled in by hand in the receipt (( 1 ) of  FIG. 11 ), the image processing apparatus  10  creates an image data that includes the handwritten text as well as the steganographic ID at the same time as embedding the data identifying the concerned person (for example, the Employee code “12345678” and the Serial No. “1234” shown in Fig.  FIG. 11 ) as the steganographic ID in the image data of the receipt (see ( 2 ) of  FIG. 11 ). At the same time as outputting the image data to the printed document, the image processing apparatus  10  forwards the entire image data to the steganographic-ID management server  20 , with a request for registration (see ( 3 ) of  FIG. 11 ).  
         [0086]     Thus, the steganographic ID is embedded in the image to be imprinted in the printed document, and image with the steganographic ID embedded therein is output to a printed document followed by registration of the output image and the steganographic ID embedded in the image imprinted in the printed document in a correlated form in the steganographic-ID management table. Thus, embedding the steganographic ID in the image data just before registering the image data and the steganographic ID in a correlated form enables prevention of any potential tampering with the steganographic ID, thus enhancing the reliability of the steganographic ID.  
         [0000]     (2) Authentication  
         [0087]     In the first embodiment, the image data corresponding to the steganographic ID embedded in the actual printed document is displayed, thus making it possible to authenticate by visual comparison of the actual printed document and the displayed image data of the printed document to determine if they match. However, authentication can also be implemented by identifying whether the actual printed document has a steganographic code embedded therein.  
         [0088]     Specifically, extraction of steganographic ID can be carried out from the printed document to be authenticated, and if the steganographic ID is extractable, the printed document can be regarded genuine, otherwise, as a counterfeit.  
         [0089]     Thus, by identifying a printed document as a counterfeit based on the inability to extract the steganographic ID from the printed document, the trouble involved in authentication by visual comparison can be done away with and authentication can be performed easily as the image imprinted in the printed document having the steganographic ID embedded therein is authenticated automatically.  
         [0000]     (3) Permissible ID  
         [0090]     In the first embodiment, the image data corresponding to the steganographic ID of the actual printed document is displayed and the actual printed document and the displayed image data of the printed document are visually compared to determine whether they match. However, authentication can be carried out by storing a permissible ID, and determining whether the steganographic ID embedded in the image imprinted in the printed document to be authenticated matches the provided permissible ID.  
         [0091]     Specifically, the steganographic-ID management server can further include a permissible ID storage unit that stores therein a permissible ID. Authentication can be carried out by extracting the steganographic ID embedded in the image imprinted in the printed document to be authenticated and determining whether the extracted steganographic ID matches the permissible ID stored in the permissible ID storage unit. If the extracted ID matches the permissible ID stored in the permissible ID storage unit, the printed document can be regarded as genuine, otherwise, as a counterfeit.  
         [0092]     Thus, by including a permissible ID storage unit that authenticates the steganographic ID as genuine is further included in the steganographic-ID management server, and performing authentication by extracting the steganographic ID imprinted in the printed document and determining whether the extracted steganographic ID matches the steganographic ID stored in the permissible ID storage unit, the image not containing the preset permissible ID are automatically rejected. As a result, the preset steganographic ID can be changed at will, making it possible to perform a more appropriate authentication.  
         [0000]     (4) System configuration.  
         [0093]     The constituent elements of each apparatus illustrated are merely conceptual and may not necessarily physically resemble the structures shown in the drawings. For instance, the apparatus need not necessarily have the structure that is illustrated. Each apparatus as a whole or in parts can be broken down or integrated either functionally or physically in accordance with the load or how the apparatus is to be used. For example, the image processing apparatus  10  and the steganographic-ID management server  20  can be integrated as a single entity. Further, the process functions performed by each apparatus are entirely or partially realized by the CPU or a program executed by the CPU or by a hardware using wired logic.  
         [0094]     All the automatic processes explained in the present embodiment can be, entirely or in part, carried out manually. Similarly, all the manual processes explained in the present embodiment can be entirely or in part carried out automatically by a known method. The process procedures, the control procedures, specific names, and data, including various parameters, can be changed as required unless otherwise specified.  
         [0000]     (5) Computer Programs  
         [0095]     Some or all of the processes, methods, or steps explained above can be realized by having a computer such as a personal computer execute a ready computer program. An example of a computer that implements the program accomplishing the function described in the present embodiment is explained with reference to  FIG. 12 .  FIG. 12  is a block diagram of a computer that implements an image authentication program.  
         [0096]     A computer  600  that functions as a steganographic-ID authentication apparatus includes a hard disk drive (HDD)  610 , a random access memory (RAM)  620 , a read-only memory (ROM)  630 , and a central processing unit (CPU)  640 , all of which are connected to a bus  650 .  
         [0097]     The ROM  630  contains ready computer programs that accomplish the functions of the steganographic-ID authentication apparatus  600 . That is, as shown in  FIG. 11 , the ROM  630  contains a steganographic-ID extraction program  631 , a registration program  632 , an authentication program  633 , a steganographic-ID embedding program  634 , and a printed-document output program  635 . The programs  631  to  635  can be separate programs or can be integrated.  
         [0098]     The CPU  640  loads and executes the programs  631  to  635  and, as shown in  FIG. 12 , performs a steganographic-ID extraction process  641 , a registration process  642 , an authentication process  643 , a steganographic-ID embedding process  644 , and a printed-document output process  645 , respectively. The processes  641  to  645  correspond to the steganographic-ID extracting unit  22   a , the registering unit  22   b , the image display unit  32   d , the steganographic-ID embedding unit  15   a , and the printed-document output unit  15   b , respectively.  
         [0099]     As shown in  FIG. 12 , The HDD  610  contains a steganographic-ID management data table  611 . The steganographic-ID management data table  611  corresponds to the steganographic-ID management table  23   a . The CPU  640  registers data in the steganographic-ID management data table  611  as well as loads steganographic-ID management data  621  from the steganographic-ID management data table  611  to the RAM  620 , and performs management of the steganographic ID based on the steganographic-ID management data  621  stored in the RAM  620 .  
         [0100]     According to an aspect of the present invention, a printed document is output after an image of a different density in the form of a code is embedded in two adjoining blocks. The code embedded in the printed document and the image imprinted in the printed document are registered in an image code storage unit. The code embedded in the printed document extracted and the image imprinted in the printed document is authenticated based on the extracted code. Consequently, the image imprinted in the printed document can be authenticated regardless of the image content in the printed document.  
         [0101]     According to another aspect of the present invention, the printed document is output after embedding only the code. Upon receipt of the printed document with the image imprinted therein, the code and the image imprinted in the printed document are registered in a correlated form in the image code storage unit. Consequently, the process of embedding the code in the image data during registration can be done away with.  
         [0102]     According to still another aspect of the present invention, the code is embedded in the image to be imprinted in the printed document and the printed document is output after the image with the code embedded therein is imprinted in the printed document. The output image and the code embedded in the image are registered in a correlated form in the image code storage unit. Consequently, by embedding the code in the image data just before registering the entire image data and the code in a correlated form enable prevention of any potential tampering with the code, thus enhancing the reliability of the code.  
         [0103]     According to still another aspect of the present invention, the code embedded in the printed document is extracted, and the image corresponding to the extracted code registered in the image code storage unit is displayed on a designated display unit, making it possible to authenticate by visual comparison of the actual printed document and the displayed image data of the printed document to determine if they match. Thus, authentication can be carried out appropriately according to requirement.  
         [0104]     According to still another aspect of the present invention, a retaining unit containing an authentic code in an authentic code storage unit is further provided. The code embedded in the printed document is extracted and if the extracted code does not match with the authentic code stored in the authentic code storage unit, the image imprinted in the printed document is certified as a counterfeit. Consequently, the preset code can be changed at will, making it possible to perform a more appropriate authentication.  
         [0105]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art that fairly fall within the basic teaching herein set forth.