Abstract:
An image data encoding system has a discrete cosine transformer for discrete cosine transforming the original image, an electronic watermark data embedding circuit for embedding the electronic watermark data in the data that has been transformed by the discrete cosine transformer, and a data selector for selecting the output signal of the discrete cosine transformer or the output signal of the electronic watermark data embedding circuit. Another image data encoding system has an electronic watermark embedding circuit for embedding electronic watermark data selected from a plurality of types of electronic watermark data to the digital image data, wherein at least one of the plurality of types of electronic watermark data is predetermined electronic watermark data that does not affect the digital image data even if the electronic watermark data is embedded in the digital image data.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a digital image processing system and, in particular, to an image data encoding system for embedding identification data with special information (hereinafter, referred to as electronic watermark data) to a digital image. In addition, the present invention relates to an image inputting apparatus for use in, for example, a personal computer and, in particular, to an image inputting apparatus equipped with an illegal copy prohibiting function. 
     2. Description of the Related Art 
     In recent years, the act of illegally copying digital images causes a social problem. 
     To prevent digital images from being illegally copied, an encryption system has been proposed. In this system, digital image data is encrypted. Only are producing system with a valid decryption key can reproduce the encrypted digital image data. However, in such a system, once encrypted data is decrypted, there is no way to prevent the data from being copied any more. 
     The purpose of a conventional illegal copy prohibiting method for an image inputting apparatus was to prevent the instance of copying image data. 
     FIG. 9 is a block diagram showing an example of an image inputting apparatus equipped with a conventional illegal copy prohibiting function. An input image is supplied to image pickup means  901 , analog-to-digital converting means  902 , converting means  903 , quantizing means  904 , and variable-length encoding means  905 . After the input image is converted into compressed image data such as an MPEG data stream, the resultant data is supplied to scrambling means  906 . Scrambling means  906  scrambles the input data and outputs compressed and scrambled image data. The compressed and scrambled image data can be reproduced only by an apparatus with a de-scrambling function. 
     As explained above, in the conventional system, images are scrambled to be prevented from being illegally copied. 
     In the conventional system, once scrambled images were descrambled, it was impossible to prevent them from being illegally copied. 
     In addition to such a conventional system, in order to prevent bills and securities from being illegally copied, a method for embedding identification information in pixel components of an image has been proposed in, for example, Japanese Patent Laid-Open Publication Nos. 4-351164, 6-22062, and 6-22119. 
     In the method for embedding identification information to pixel components of an image, there was the disadvantage that the identification information could be easily forged and removed. 
     Therefore, a method for embedding electronic watermark data in a digital image has been proposed to prevent digital images from being illegally used and copied. 
     There are two types of electronic watermark data for digital images, i.e. visible electronic watermark data and invisible electronic watermark data. 
     The visible electronic watermark data is composed of special characters or symbols so that it can be recognized by visual sensation. Although the visible electronic watermark data causes deterioration of the image quality, the user of the digital image can distinguish it from a forged one, whereby illegal circulation of bills or securities can be prevented. 
     An example of a method for embedding visible electronic watermark data in an electronic image is disclosed in Japanese Patent Laid-Open Publication No. 8-241403. In this method, when visible electronic watermark data is combined with an original image, only the brightness of pixels corresponding to an opaque portion of the electronic watermark data is varied, not color components. In this method, scaling values which vary the brightness components of the pixels are determined corresponding to color components, random numbers, pixel values of electronic watermark data, or the like. 
     On the other hand, the invisible electronic watermark data is embedded in an image in such a manner that the electronic watermark data does not affect the image quality. Thus, since the invisible electronic watermark faintly deteriorates the image quality, the deterioration is not perceivable by visual sensation. When special information that identifies a copyright holder of a original image is embedded in the form of the electronic watermark data, even after the image has been illegally copied, the copyright holder of the image can be identified by detecting the electronic watermark data. In addition, in the case that information inhibiting duplication is embedded in a image in the form of electric watermark data, when a relevant reproducing unit such as VTR detects the information, the unit can inform the user that the duplication of the image is inhibited or the unit can prevent duplication of the image by activating duplication inhibiting mechanism. 
     As one method for embedding invisible electronic watermark data in a digital image, special information representing invisible electronic watermark is embedded in a portion where the information faintly affects the picture quality such as the least significant bits (LSBs) of pixel data. However, in this method, it is easy to erase the electronic watermark data from the image. For example, with a low-pass filter, the information of LSBs of the pixel data can be removed. Additionally, in the image compressing process, redundant data that faintly affects the image quality is removed so as to reduce the data amount and the electric watermark data is embedded in the place where redundant data exists. Thus, when the image compressing process is performed, the electronic watermark data is lost. Consequently, it is difficult to detect the electronic watermark data of an image that has been compressed. 
     To solve this problem, a method for transforming an image into frequency components and embedding electronic watermark data in the frequency spectrum has been proposed (Nikkei Electronics, p. 13, No. 660, Apr. 22, 1996). In this method, since electronic watermark data is embedded in frequency components, even if an image process such as a compressing process or a filtering process is performed for an image, the electronic watermark data is not lost. In addition, when random numbers that follow a normal distribution are used as electronic watermark data, different pieces of electronic watermark data do not interfere with each other. Thus, it is difficult to destroy the electronic watermark data without largely deteriorating the image. 
     Referring to FIG. 10, the method for embedding electronic watermark data in an image is performed as follows. First of all, a discrete cosine transforming means  1020  transforms an original image into frequency components. In the frequency components, n components are selected as f( 1 ), f( 2 ), . . . , f(n) according to amplitude order. Electronic watermark data pieces w( 1 ), w( 2 ), . . . , w(n) are extracted from random data following a normal distribution with means=0 and variance=1. An electronic watermark data embedding means  1030  calculates the following equation for each i: 
       F ( i )= f ( i )+α| f ( i )|· w ( i ), 
     where 1≦I≦n and where α is a scaling factor. Finally, image data in which electronic watermark data has been embedded is obtained by transforming F(I) by inverse discrete cosine transform. 
     The electronic watermark data is detected in the following manner. In this case, it is assumed that the original image and electronic watermark data candidate set {w(i)} (where i=1, 2, . . . , n) are known. 
     With reference to FIG. 11, a discrete cosine transforming means  1120  transforms an image in which electronic watermark data has been embedded into frequency components F( 1 ), F( 2 ), . . . , F(n). A discrete cosine transforming means  1110  transforms original image data into frequency components f( 1 ), f( 2 ), . . . , f(n). With f(i) and F(i), electronic watermark data estimated values W(i) are calculated and extracted by the following equation: 
     
       
           W ( i )=( F ( i )− f ( i ))/ f ( i ). 
       
     
     Next, an inner product calculating means  1140  calculates the statistical similarity of w(i) and W(i) by the following equation: 
     
       
           C=W*w/ ( WD*wD ), 
       
     
     where W=(W( 1 ), W( 2 ), . . . , W(n)); w=(w( 1 ), w( 2 ), . . . , w(n)); WD=absolute value of vector W; and wD=absolute value of vector w. A statistical similarity determining means  1160  determines that relevant electronic watermark data has been embedded in a relevant image when the value of C is equal to or larger than a predetermined value. 
     If the copyright holder of images embeds electronic watermark data in the images, the electronic watermark data is effective to check out images that the holder doubts is illegally copied. FIG. 12 is a block diagram showing an image data encoding system with such an electronic watermark data embedding means according to a related art reference. Discrete cosine transforming means  1201  orthogonally transforms the original image data in time domain into data in frequency domain. Electronic data embedding means  1202  embeds electronic watermark data  1203  in the data in frequency domain. Quantizing means  1204  quantizes the data in which the electronic watermark data has been embedded. Encoding means  1205  encodes the quantized data and outputs the resultant MPEG data. 
     The aforementioned conventional encoding system always embeds electronic watermark data in a relevant image. Although the image faintly deteriorates as the electronic watermark data is embedded in frequency components, it is not that the image does not at all deteriorate. Therefore, another image encoding system having no means for embedding electric watermark data is required when image should not be embedded with electric watermark data, especially when the quality of the image should be valued. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide an encoding system that generates not only encoded data of image in which electric watermark data is embedded but also encoded data of image in which electric watermark data is not embedded. 
     Another object of the present invention is to provide an image inputting apparatus that generates not only encoded data of image in which electric watermark data is embedded but also encoded data of image in which electric watermark data is not embedded. 
     According to one aspect of the present invention, there is provided an image data encoding system for embedding electronic watermark data to an original image, which comprises: discrete cosine transforming means for discrete-cosine transforming the original image; electronic watermark data embedding means for embedding the electronic watermark data in the data that has been transformed by the discrete cosine transforming means; and data selecting means for selecting the output signal of the discrete cosine transforming means or the output signal of the electronic watermark data embedding means. 
     The image data encoding system further comprises: a flip-flop connected to the data selecting means, wherein the data selecting means selects the output signal of the discrete cosine transforming means or the output signal of the electronic watermark data embedding means corresponding to information stored in the flip-flop. 
     In the image data encoding system, the data selecting means selects the output signal of the discrete cosine transforming means or the output signal of the electronic watermark data embedding means corresponding to an external signal. 
     According to another aspect of the present invention, there is provided an image data encoding system for encoding digital image data in a predetermined encoding manner and outputting the resultant image data, which comprises: an electronic watermark embedding means for embedding electronic watermark data selected from a plurality of types of electronic watermark data to the digital image data, wherein at least one of the plurality of types of electronic watermark data is predetermined electronic watermark data that does not affect the digital image data even if embedded in the digital image data. 
     In the image data encoding system, the predetermined electronic watermark data is composed of other than random numbers generated by an algorithm corresponding to a normal distribution. 
     The image data encoding system further comprises: transforming means for transforming the digital image data into frequency components and outputting the resultant data to the electronic watermark data embedding means; quantizing means for quantizing the data in which electronic watermark data has been embedded by the electronic watermark data embedding means; and a variable-length encoding means for encoding output data of the quantizing means into variable-length code. 
     According to still another aspect of the present invention, there is provided an image data encoding system for encoding digital image data in a predetermined manner and outputting the resultant data, comprising: a plurality of electronic watermark data tables having a plurality of types of electronic watermark data for identifying the digital image data; an electronic watermark data selecting means for selecting one of the electronic watermark data tables; and an electronic watermark data embedding means for embedding the selected type of electronic watermark data in the digital image data, wherein at least one of the electronic watermark data tables has a predetermined electronic watermark data that does not affect the digital image data even if embedded in the digital image data. 
     In the image data encoding system, the predetermined electronic watermark data is composed of other than random numbers generated by an algorithm corresponding to a normal distribution. 
     The image data encoding system further comprises transforming means for transforming the digital image data into frequency components and outputting the resultant data to the electronic watermark data embedding means; a quantizing means for quantizing the data in which electronic watermark data has been embedded by the electronic watermark data embedding means; and a variable-length encoding means for encoding output data of the quantizing means into variable-length code. In the image data encoding system, the predetermined electronic watermark data is composed of other than random numbers generated by an algorithm corresponding to a normal distribution. 
     According to the further aspect of the present invention, there is provided an image inputting apparatus, which comprises: image pickup means for obtaining an analog image signal; analog-to-digital converting means for converting the analog image signal obtained by the image pickup means into image data; transforming means for transforming the image data into data in first frequency domain; storing means for temporarily storing the data in the first frequency domain; identification data holding means for holding identification data; means for adding the identification data to the data in the first frequency domain and generating data in second frequency domain; and selecting means for selecting either of the data in the first frequency domain and the data in the second frequency domain and outputting the selected data. 
     In the image inputting apparatus, the transforming means is an orthogonal transforming means. 
     The image inputting apparatus further comprises: compressing means for compressing and encoding the output signal of the selecting means. 
     According to still further aspect of the present invention, there is provided an image inputting apparatus, comprising: image pickup means for obtaining an analog image signal; analog-to-digital converting means for converting the analog image signal obtained by the image pickup means into image data; transforming means for transforming the image data into data in first frequency domain; storing means for temporarily storing the image data; identification data holding means for holding identification data; means for adding the identification data to the data in the first frequency domain and generating data in second frequency domain; inverse-transforming means for inversely transforming the data in the second frequency domain into data in time domain; and selecting means for selecting either of the output signal of the inverse-transforming means and the output signal of the storing means. 
     In the image inputting apparatus, the transforming means is an orthogonal transforming means and the orthogonal inverse-transforming means is an orthogonal inverse-transforming means. 
     The image inputting apparatus, further comprises: compressing means for compressing and encoding the output signal of the selecting means. 
     These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of a best mode embodiment thereof, as illustrated in the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram showing the structure of an image data encoding system according of a first embodiment of the present invention; 
     FIG. 2 is a block diagram showing the structure of an image data encoding system according to a first example of the present invention; 
     FIG. 3 is a block diagram showing the structure of an image data encoding system according to a second example of the present invention; 
     FIG. 4 is a block diagram showing the structure of an image data encoding system according of a second embodiment of the present invention; 
     FIG. 5 is a block diagram showing the structure of an image inputting apparatus according to a third embodiment of the present invention; 
     FIG. 6 is a block diagram showing the structure of an image inputting apparatus according to a third example of the present invention; 
     FIG. 7 is a schematic diagram for explaining an embedment of identification data in frequency domain according to the third example of the present invention; 
     FIG. 8 is a block diagram showing the structure of an image inputting apparatus according to a fourth example of the present invention; 
     FIG. 9 is a block diagram showing an example of the structure of a conventional image inputting apparatus; 
     FIG. 10 is a block diagram for explaining an electronic watermark data embedding method according to a related art reference; 
     FIG. 11 is a block diagram for explaining an electronic watermark data detecting method according to a related art reference; and 
     FIG. 12 is a block diagram showing the structure of an image data encoding system according to a related art reference. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     Next, with reference to the accompanying drawings, embodiments and examples of the present invention will be explained. 
     First Embodiment of Present Invention 
     With reference to FIG. 1, an image data encoding system according to a first embodiment of the present invention comprises discrete cosine transforming means  101 , electronic watermark data embedding means  102 , electronic watermark data  103 , data selecting means  106 , quantizing means  104 , and encoding means  105 . Discrete cosine transforming means  101  transforms input original image data in time domain into data in frequency domain. Electronic watermark data embedding means  102  embeds electronic watermark data  103  in the data in frequency domain. Data selecting means  106  alternatively selects output signal  107  of discrete cosine transforming means  101  or output signal  108  of electronic watermark data embedding means  102 . Quantizing means  104  quantizes data selected by data selecting means  106 . Encoding means  105  encodes the quantized data received from quantizing means  104  and generates MPEG data. 
     Next, the operation of the system shown in FIG. 1 will be explained. 
     Discrete cosine transforming means  101  converts the original image data in time domain into data in frequency domain. Electronic watermark data embedding means  102  embeds electronic watermark data  103  in the data in frequency domain. 
     Output signal  108  of electronic watermark data embedding means  102  is supplied to one input terminal of data selecting means  106 . Output signal  107  of discrete cosine transforming means  101  is supplied to an input terminal of electronic watermark data embedding means  102 . In addition, output signal  107  is supplied to the other input terminal of data selecting means  106 . When the electronic watermark data  103  should be embedded in the original image data, data selecting means  106  selects output signal  108 . When the electronic watermark data  103  should not be embedded in the original image data, data selecting means  106  selects output signal  107 . 
     Quantizing means  104  quantizes the data selected by data selecting means  106 . Encoding means  105  encodes the quantized data and outputs MPEG data. 
     First Example of Present Invention 
     Next, with reference to FIG. 2, a first example according to the first embodiment of the present invention will be explained. 
     With reference to FIG. 2, output signal  107  of discrete cosine transforming unit  101  or output signal  108  of electronic watermark data embedding unit  102  is alternatively selected by selecting unit  110  that operates corresponding to information stored in flip-flop  111 . When the electronic watermark data should not be embedded in the image data, a logic value “0” is stored in flip-flop  111 . When the electronic watermark data should be embedded in the original image data, a logic value “1” is stored in flip-flop  111 . 
     Discrete cosine transforming unit  101  orthogonally transforms original image data in time domain into data in frequency domain. Electronic watermark data embedding unit  102  embeds electronic watermark data  103  in the data in frequency domain. 
     Output signal  108  of electronic watermark data embedding unit  102  is supplied to one input terminal of selecting unit  110 . Output signal  107  of discrete cosine transforming unit  101  is supplied to an input terminal of electronic watermark data embedding unit  102 . In addition, output signal  107  of discrete cosine transforming unit  101  is supplied to the other input terminal of selecting unit  110 . When the information of flip-flop  111  represents the logical value ‘0’, selecting unit  110  selects output signal  107 . When the information of flip-flop  111  represents the logical value ‘1’, selecting unit  110  selects output signal  108 . 
     Quantizing unit  104  quantizes the data selected by selecting unit  110 . Encoding unit  105  encodes the quantized data and outputs MPEG data. 
     Second Example of Present Invention 
     Next, with reference to FIG. 3, a second example according to the first embodiment of the present invention will be explained. 
     Referring to FIG. 3, output signal  107  of discrete cosine transforming unit  101  and output signal  108  of electronic watermark data embedding unit  102  is alternatively selected by selecting unit  110  corresponding to external signal  112 . When electronic watermark data  103  should not be embedded in image data, a logical value ‘0’ is set to external signal  112 . When electronic watermark data should be embedded in image data, a logical value ‘1’ is designated to external signal  112 . 
     Discrete cosine transforming unit  101  orthogonally transforms original image data in time domain into data in frequency domain. Electronic watermark data embedding unit  102  embeds electronic watermark data  103  in the data in frequency domain. 
     Output signal  108  of electronic watermark data embedding unit  102  is supplied to one input terminal of selecting unit  110 . Output signal  107  of discrete cosine transforming unit  101  is supplied to an input terminal of electronic watermark data embedding unit  102 . In addition, output signal  107  is supplied to the other input terminal of selecting unit  110 . When external signal  112  represents the logical value ‘0’, selecting unit  110  selects output signal  107 . When external signal  112  represents the logical value ‘1’, selecting unit  110  selects output signal  108 . 
     Quantizing unit  104  quantizes the data selected by selecting unit  110 . Encoding unit  105  encodes the quantized data and outputs MPEG data. 
     Second Embodiment of Present Invention 
     Next, with reference to FIG. 4, an image data encoding system according to a second embodiment of the present invention will be explained. 
     FIG. 4 is a block diagram showing the structure of the image data encoding system according to the second embodiment of the present invention. In FIG. 4, the image data encoding system comprises discrete cosine transforming means  402 , a plurality of electronic watermark data tables  408  ( 0 ),  408 ( 1 ),  408 ( 2 ) . . .  408 (n), electronic watermark data selecting unit  407 , electronic watermark data embedding means  404 , quantizing means  405 , and encoding means  406 . Discrete cosine transforming means  402  performs a discrete cosine transforming process for original image stream  401  to be encoded. Electronic watermark data tables  408 ( 0 ),  408 ( 1 ),  408 ( 2 ), . . . ,  408 (n) have respective electronic watermark data. Electronic watermark data selecting unit  407  selects one of electronic watermark data tables  408 ( 0 ),  408 ( 1 ),  408 ( 2 ), . . . ,  408 (n). Electronic watermark data embedding means  404  embeds electronic watermark data in the data that is received from discrete cosine transforming means  402  and then temporarily stored in buffer  410 . Quantizing means  405  quantizes data received from electronic watermark data embedding means  404 . Encoding means  406  encodes data received from quantizing means  405  into variable-length code and outputs resultant MPEG data  409 . 
     Among the plurality of electronic watermark data tables  408 ( 0 ) to  408 (n), watermark data table  408 ( 0 ) has electronic data that does not affect digital image data. In other words, the electronic watermark data table  408  ( 0 ) does not have random numbers generated by an algorithm of generating random numbers in a normal distribution. On the other hand, electronic watermark data tables  408 ( 1 ) to  408 (n) have random numbers generated by the algorithm. 
     Next, the operation of the image data encoding system according to the second embodiment of the present invention will be explained. 
     First of all, the case in which normal electronic watermark data is embedded in image data will be explained. Original image data  401  is extracted in the unit of (8×8 pixel) block. Discrete cosine transforming means  402  performs a discrete cosine transforming process for the extracted data and then transforms the data into frequency components. Electronic watermark data selecting means  407  selects electronic watermark data from one of the electronic watermark data tables  408 ( 1 ) to  408 (n) except for electronic watermark data table  408 ( 0 ) and outputs the selected electronic watermark data to electronic watermark data embedding means  404 . Electronic watermark data embedding means  404  embeds the selected electronic watermark data in the frequency components. Quantizing means  405  quantizes data received from electronic watermark data embedding means  404 . Encoding means  406  encodes quantized data and outputs resultant MPEG data  409 . 
     Next, the case in which encoded data corresponding to original data is required is explained. Similarly to the normal case, original image data  401  is extracted in the unit of (8×8 pixel) block corresponding to the conventional MPEG compressing process. Discrete cosine transforming means  402  performs a discrete cosine transforming process for the extracted data and then transforms the extracted data into frequency components. Electronic watermark data selecting means  407  selects electronic watermark data that does not affect digital image data from the electronic watermark data table  408 ( 0 ) and outputs the selected electronic watermark data to electronic watermark data embedding means  404 . Electronic watermark data embedding means  404  embeds the selected electronic watermark data in the frequency components. Quantizing means  405  quantizes the data received from electronic watermark data embedding means  404 . Encoding means  406  encodes the quantized data and outputs resultant MPEG data  409 . 
     Third Embodiment of Present Invention 
     Next, with reference to FIG. 5, the basic structure of an image inputting apparatus according to a third embodiment of the present invention will be explained. With reference to FIG. 5, the image inputting apparatus comprises image pickup means  501 , analog-to-digital converting means  502 , transforming means  503 , storing means  507 , identification data holding means  510 , identification data embedding means  509 , data selecting means  508 , quantizing means  504 , and encoding means  505 . Image pickup means  501  picks up an external image. Analog-to-digital converting means  502  converts an analog signal of the picked-up image into digital image data. Transforming means  503  transforms the image data in space domain into data in frequency domain. Storing means  507  temporarily stores the image data in frequency domain. Identification data holding means  510  holds identification data. Identification data embedding means  509  embeds the identification data in the image data in frequency domain. Data selecting means  508  selects an output signal of storing means  507  or an output signal of identification data embedding means  509 . Quantizing means  504  quantizes image data. Encoding means  505  encodes the quantized image data into variable-length code. 
     Next, the operation of the image inputting apparatus according to the third embodiment of the present invention will be explained. Image pickup means  501  picks up an external image and outputs the analog signal of the picked-up image. Analog-to-digital converting means  502  converts the analog signal into digital image data and outputs the digital image data. Transforming means  503  orthogonally transforms the image data in space domain into image data in frequency domain and outputs the resultant image data. Storing means  507  temporarily stores the image data in frequency domain. Identification data holding means  510  holds and outputs identification data. Identification data embedding means  509  embeds the identification data in the image data in frequency domain and outputs the resultant data. Data selecting means  508  selects an output signal of storing means  507  or an output signal of identification data embedding means  509  and outputs the selected signal. The quantizing means  504  quantizes the image data and outputs the resultant data. The encoding means  505  encodes the quantized image data into variable-length code and outputs compressed image data. 
     Third Example of Present Invention 
     Next, with reference to FIG. 6, a third example according to the third embodiment of the present invention will be explained. Referring to FIG. 6, CCD image pickup device  601  picks up an external image and outputs the analog signal of the picked-up image. Analog-to-digital converting unit  602  converts the analog signal into digital image data and outputs the digital image data. 
     Discrete cosine transforming unit  603  orthogonally transforms the image data in space domain into data in frequency domain. Buffer  607  temporarily stores image data in frequency domain. Identification data table  610  holds and outputs identification data. Identification data embedding unit  609  embeds the identification data in the image data in frequency domain and outputs the resultant data. 
     Selecting unit  608  alternatively selects an output signal of buffer  607  or an output signal of identification data embedding unit  609 . When the output signal of buffer  607  is selected, the original image data is output. When the output signal of identification data embedding unit  609  is selected, image data in which the identification data is embedded is output. 
     Quantizing unit  604  quantizes image data and outputs the quantized image data. Variable-length encoding unit  605  encodes the quantized image data in variable-length code and outputs the resultant MPEG data. The MPEG data is supplied to for example a personal computer, a storage medium processing unit (such as an optical magnetic medium), a network processing unit (that transmits the data to a network line), or a radio media processing unit (that transmits the data to a radio channel). 
     Next, with reference to FIG. 7, an embedding method of identification data will be explained. When image data in space domain is orthogonally transformed into data in frequency domain by discrete cosine transforming unit  603 , a frequency spectrum  701  shown in FIG. 7 is generated. Identification data table  610  outputs the identification data with a frequency spectrum  704  shown in FIG.  7 . Frequency spectrum  704  is similar to the spectrum  701 . When adding unit  702  adds frequency spectrum  704  of the identification data to frequency spectrum  701  of the original image, a frequency spectrum  703  in which the identification data is embedded is obtained. 
     To extract the identification data, a subtracting unit (not shown) extracts frequency spectrum  701  of the original image from frequency spectrum  703  in which the identification data is embedded and obtains frequency spectrum  704  of the identification data. Thus, the identification data can be easily extracted. 
     Fourth Example of Present Invention 
     Next, with reference to FIG. 8, a fourth example according to the third embodiment of the present invention will be explained. Referring to FIG. 8, CCD image pickup device  601  picks up an external image and outputs the analog signal of the picked-up image. Analog-to-digital converting unit  602  converts the analog signal into digital image data and outputs the image data. Buffer  807  temporarily stores the digital image data. 
     Discrete cosine transforming unit  603  orthogonally transforms image data in space domain into data in frequency domain and outputs the resultant data. Identification data table  610  holds and outputs identification data. Identification data embedding unit  609  embeds the identification data in the image data in frequency domain and outputs the resultant data. Inverse discrete cosine transforming unit  811  transforms the image data in frequency domain into data in space domain and outputs the resultant image data. The image data in frequency domain may be converted into the image data in space domain by fast Fourier transforming method rather than the discrete cosine transforming method. 
     Selecting unit  808  alternatively selects the output signal of buffer  807  or the output signal of inverse discrete cosine transforming unit  811 . When the output signal of buffer  807  is selected, the original image data is output. When the output signal of inverse discrete cosine transforming unit  811  is selected, the image data in which the identification data is embedded is output. 
     Since the embedding method of the identification data according to the fourth example is the same as that of the third example, the description thereof is omitted. To extract the identification data, the discrete cosine transforming means orthogonally transforms the image data in space domain into the image data in frequency domain. Thereafter, a subtracting unit (not shown) subtracts the frequency spectrum of the original image data from the frequency spectrum in which the identification data is embedded and obtains the frequency spectrum of the identification data. 
     As explained above, according to the present invention, since both image data with electronic watermark data and image data without electronic watermark data can be encoded by one encoding system rather than two encoding systems, the hardware scale can be remarkably reduced. 
     According to the present invention, even if image data is illegally copied, it can be identified. This is because identification data has been embedded in the image data. Thus, by detecting the identification data, the route of the illegal copy can be tracked. 
     In addition, when identification data is deleted or destroyed and thereby original image data thereof is illegally copied, the image quality of the image data remarkably deteriorates. Thus, the image data can be prevented from being illegally forged and copied. 
     Although the present invention has been shown and explained with respect to a best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions, and additions in the form and detail thereof may be made therein without departing from the spirit and scope of the present invention.