Method and apparatus for imprinting ID information into a digital content and for reading out the same

After a digital content is loaded into an information terminal such as a PC, ID information unique to a viewer or a user of the PC is imprinted into the content. The ID information is imprinted into a predetermined location of the content or alternatively, it may be imprinted over the entire content in the form of a spatial frequency. The content with an ID added thereto is then enabled to be used in the terminal.

This invention relates to a method for imprinting identification information (ID) into a digital content and for reading that information.

BACKGROUND

The information superhighway was advocated in the United States in 1991, and since then distribution of information over networks as represented by the Internet has been forming a new society base. In this new network society, secure encryption and authentication are desired in such fields as electronic commerce because such fields are concerned with safety.

On the other hand, one of the principles of the Internet is the free distribution of digital contents such as pictures, animation and music (hereinafter collectively referred to as contents). Presently, even for valuable content, such as cultural works, illegal copies can be easily made and distributed. Collecting fees for using contents on the Internet, preventing illegal reproduction or modification, and protecting copyrights are serious problems that need to be addressed and solved. These issues are extremely important for the mutual development of a network society and culture.

It is therefore desired to design a general approach to trace illegal copies of digital contents.

SUMMARY

It is the object of this invention to provide an identification (ID) imprinting method applicable to existing contents.

It is a further object of this invention to provide an ID imprinting method applicable to a content having no reserved areas or areas for remarks that do not play any role in the content.

It is still another object of this invention to provide an ID imprinting method which does not introduce substantial degradation of the content quality when an ID information is imprinted.

It is yet another object of this invention to provide an ID imprinting method for embedding an ID information that can be easily detected.

It is yet another object of this invention to provide an ID readout method to easily detect and interpret the ID information imprinted in the content.

A method according to an embodiment of the present invention comprises loading a content into an information terminal where the content is used and imprinting an ID information associated to the information terminal or its user into a predetermined location in a perceivable portion of the loaded content. (A content may be any collection of digital data, and may be in the form of a sequence of data values. A perceivable portion contains data that play a role in the content, rather than reserved areas or areas for remarks that do not play any role in the content.)

The content is first loaded into an information terminal. Subsequently, an ID information is imprinted into a predetermined location of the content. A user who reproduces illegal copies of the content is identified with the ID information imprinted therein. Since the ID information is imprinted in a predetermined location, no string search is necessary. This method is applicable to existing contents, since it requires no special data blocks beforehand.

In another aspect of the invention, an ID information is imprinted in the form of spatial frequency information into the entire content loaded into an information terminal. “Spatial frequency information” is information relative to a spatial frequency in any sense. In this aspect, the ID information is converted into spatial frequency information via, for instance, an inverse orthogonal transformation so as to be reflected in the content data. The inverse orthogonal transformation may be an inverse fast Fourier transform (IFFT) or an inverse discrete cosine transform (IDCT). This method is also applicable to existing contents.

According to the ID reading process of this invention, a content is first obtained for instance via a network, and an ID information is read from a predetermined location thereof. The ID information is uniquely associated with an information terminal or its user. In another aspect, spatial frequency information is extracted from the obtained content, and then supplied for an orthogonal transformation. Through the transformation, the ID information imprinted in the content is restored. An orthogonal transformation may be a fast Fourier transform (FFT), a discrete cosine transform (DCT), and so forth.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention may be applied to a network system comprising a server2and client devices connected on a network9, as shown in FIG.1. In this drawing, client devices include PCs4and8and a Personal Digital Assistance (PDA)6, which are information terminals.

The server2supplies a content to the client devices so that ID imprinting is carried out on the client side. Here, as an example, the PC4is provided with an imprinting function.

FIG. 2is an operational flowchart of the PC4when it receives a content. The PC4first downloads the content from the server2over the network9(S0). A program for decoding or decrypting the content is also downloaded from the server. This program may be included in a downloaded viewer or browser that turns the encrypted content into a usable form. A user ID information associated with the PC4or its user is embedded in the viewer. The ID is imprinted in the content when the viewer decodes the content (S2). After the ID is imprinted, use of the content such as for displaying or copying is enabled.

FIG. 3shows the structure relating to ID imprinting within the PC4. In the following example, the content is assumed to be an image. The user first sends a request for a content to a content manager or supplier (not shown) which runs the server2. The content manager, after authentication of the user, transmits the requested content and a viewer12to the PC4via the network. These are received by a communication section10of the PC4.

The viewer12received in the PC4may now be used to decrypt and display the received content. As shown inFIG. 3, the content is inputted to the viewer12. The viewer12comprises an image decoder14for decoding an image which has been compressed or encoded by the content manager before transmission to the PC4, an ID holder16for storing IDs, and an ID imprinter18for imprinting the ID read from the ID holder16onto a decoded image. The image decoder14has a decryption algorithm. The content manager transmits the viewer12after storing an ID unique to the user requesting the content in the ID holder16. The viewer12may be a plug-in type device that is incorporated into existing Internet browsers.

As a measure for preventing use of content before ID imprinting, for instance, a memory area in the PC4that stores a content without an ID imprinted therein is protected by the ID imprinter18so that reading of such a content is prevented. Specifically, the system is designed so as to be interrupted or reset if a read access is made to the memory area containing a content without an ID. Once an ID is imprinted, this protection is removed, enabling the image to be used as desired.

As shown inFIG. 3, an image having an ID imprinted therein is transmitted to a display controller20, where it is converted into display format for a display24. A memory controller22writes data to a storage device26, which may be a hard disc unit or the like, to store the decoded image therein.

FIG. 4is a diagram showing an internal structure of the ID imprinter18shown inFIG. 3according to one embodiment of the present invention. The imprinter18comprises an ID reader30for reading an ID from the ID holder16, a decoded image reader32for reading a decoded image, and a combiner34for imprinting an ID into a predetermined location such as the leading, middle, or trailing part of the decoded image data. When an ID consists of n bits of data and the luminance of image pixels in the content is expressed in multiscale, the combiner34for instance sequentially replaces the least significant bits (LSBs) of the luminance of n pixels from the leading part of the image by the n bits of ID data.

In operation, the user of the PC4requests the server2run by the content manager to transmit a content. The content is encrypted on the server2and then sent with the viewer12to the PC4via a network. The communication section10of the PC4receives the transmitted content, and forwards it to the viewer12, which has been received from the network. Within the viewer12, the image decoder14decodes the content, and forwards it to the ID imprinter18. The ID reader30in the ID imprinter18reads the ID from the ID holder16and supplies it to the combiner34. The decoded image reader32reads the decoded image, and forwards it to the combiner34. Having received the ID and the decoded image, the combiner34replaces the LSBs of the luminance in the aforementioned manner to thereby imprint the ID onto the image. The image having the ID is displayed on the display24. The ID imprinted image may also be supplied to the memory26. If a subsequent unauthorized attempt is made to modify or reproduce the ID-imprinted image stored in the memory26, copies of such modified or reproduced image will carry the ID information imprinted in the image stored in the memory26. It is therefore possible to identify the party making the unauthorized copies.

FIG. 5is a diagram showing an alternative structure of the ID imprinter18according to another embodiment of the present invention. In this figure, the same members as shown inFIG. 4are given the same reference numerals and their explanation is not repeated. The structure inFIG. 5comprises an IFFT section40for performing an inverse fast Fourier transform (IFFT) on a signal representing an ID, and a combiner42for combining the transformed ID (i.e. the output of the IFFT section40) into the decoded image.

In this embodiment, the ID information is represented as a signal in the frequency domain. When imprinting such an ID, an inverse orthogonal transform is applied to the frequency signal representing the ID information to generate a bit pattern in the content domain, which is then imprinted in the digital content. In this specification, the term “content domain” is used to denote the domain representing the data in the digital content, while the term “frequency domain” is used to denote a mapping of the content domain through an orthogonal transform. When the content is a two-dimensional image (an example used in the illustration below), the content domain is a two-dimensional space domain, and the corresponding frequency domain is a two-dimensional spatial frequency domain. When the content is audio, the content domain may be a time domain and the frequency domain may be a one-dimensional frequency domain.

FIG. 6is a diagram showing examples of representations of ID information as signals in the frequency domain. A two-dimensional image is used as an example of a content. The rectangle52represents a two-dimensional spatial frequency domain for the two-dimensional space domain. The arrows54aand54bindicate the x and y directions of the corresponding space domain, whereas the arrows56aand56bindicate the directions of increased frequencies in the frequency domain corresponding to the x and y directions of the space domain, respectively. In this frequency domain, signals representing the ID information for three users A, B, and C are plotted at their respective positions (xa, ya), (xb, yb), and (xc, yc). For user A, for example, the frequency signal has a steep peak centered at the point (xa, ya). The steep peak may have finite widths, or it may be a delta-function. In this manner, the ID information for a user is represented by a point in a two-dimensional frequency domain.

FIG. 7is a diagram showing user A's ID information converted into a bit pattern in the space domain by the IFFT section40. The pixels in the bit pattern showing inFIG. 7have a value of “1” in the shaded areas and “0” in the unshaded areas. In this example, since the frequency signal representing user A's ID information is located substantially at the center of the spectrum domain with respect to both the x and y directions (see FIG.6), the spatial frequencies of the shaded and unshaded areas shown inFIG. 7are more or less the same in the x and y directions. For user B, for example, since the frequency signal representing that user's ID information has higher frequencies in both directions, the shaded and unshaded areas in the resulting bit pattern will be narrower (not shown).

FIG. 8is a diagram explaining a method for imprinting a bit pattern containing ID information, such as that shown inFIG. 7, onto the decoded image (the digital content). In this example, luminance values of the pixels of the decoded image are expressed in eight-bit binary data. The ID information is imprinted in the decoded image by replacing the LSB of the luminance value of each pixel by the value of the corresponding pixel in the bit pattern containing the ID information. Thus, in this example, the LSB of a pixel in the decoded image located in an area corresponding to a shaded area inFIG. 7is replaced by “1”, and the LSB of a pixel located in an area corresponding to a unshaded area inFIG. 7is replaced by “0.” The remaining seven bits of the luminance value of the pixel are unchanged from the decoded image. Thus, in this embodiment, an ID is imprinted over the entire image or an extended portion thereof. This method is advantageous as a countermeasure against partial cut-off of the content, as the extended portion over which the ID is imprinted may be chosen such that the cut off of which would substantially impair the usefulness of the content.

Specific embodiments of the present invention for imprinting ID information have been described. Many variations of the embodiments are possible, some of which are described below.

First, although a content is distributed via a network in the above-described embodiments, the content may also be distributed by storing it in a medium such as a CD-ROM or a floppy disc and loading it onto a PC. The embodiments described above are applicable to such other methods of content distribution.

Second, although a still image is used in the above-described embodiments as an example of a digital content, the methods may be applied to other types of digital content, such as motion images (e.g. video) or audio content. For motion images, ID information may be divided into plural portions and different portions may be imprinted into different image frames. For audio content, the image decoder14, the display controller20, and the display24inFIG. 3may be replaced by an audio decoder, an audio output controller, and a speaker, respectively. Further, one-dimensional IFFT is sufficient for audio content, as it is one dimensional data. In addition, although ID information is imprinted into the bits of the luminance values in the case of images, it may be imprinted into the LSBs of frequency signals or the like in the case of an audio content.

Third, an ID is not necessarily stored in the LSBs of a content. Any bits of quantified data may store the ID as long as the effects on the perceived quality of the content are insignificant. It should be noted that even perceptible imprinting may be employed as a visual watermark.

Fourth, although an ID is imprinted into a lower bit irrespective of upper bits in the aforementioned embodiment, an offset may be given to a lower bit such that the whole data including upper bits contains the ID.

FIG. 13shows an example of a 3×3 pixel area in a content such as an image, where the luminance of the respective pixels are “10, 8, 0 . . . ” as shown.FIG. 14is a diagram showing the luminance of the same 3×3 pixel area in the image, but expressed using modulo 3 arithmetic. Using this arithmetic, the corresponding value of a pixel whose luminance is 10, for instance, becomes 1.FIG. 15is a diagram showing a sample data pattern representing ID information, generated using methods described earlier, to be imprinted into the 3×3 pixel area of the image shown in FIG.14. The ID pattern is also expressed in modulo 3 arithmetic. In this example, 0's, 1's, and 2's are to be imprinted into the first, second, and third rows of pixels, respectively.FIG. 16is a diagram showing the state in which an offset of −1, 0, or 1 is added to each pixel value of the 3×3 pixel area shown inFIG. 14to obtain the corresponding pixel value of the 3×3 pixel area shown in FIG.15. In operation, the ID information is imprinted into the 3×3 pixel area of the image shown inFIG. 13by adding to each pixel an offset value −1, 0 or 1 according to the calculation shown in FIG.16. According to this method, an offset is added to the luminance data as a whole, so that the whole data, including the upper bits, contain the ID.

Since this method can prevent direct exposure of an ID unlike imprinting it in the lower bits, security is increased. Another advantage is that data other than “0” and “1”, such as “2”, is also imprintable. Although modulo 3 arithmetic is mentioned here, modulo arithmetic based on other numbers may be used. Any other mathematical, boolean algebraic or cryptographic approach may be employed.

Fifth, in the aforementioned embodiments, the combiner34(FIG. 4) imprints ID information into a predetermined location such as the leading part of the data sequence. The predetermined location may be one where, when slight shifts in data values are given, the effects are hardly perceivable. Thus, the quality of the content (quality of a still image, motion image, sound, text and so forth) is hardly influenced.

Sixth, in the embodiment shown inFIG. 3, the image decoder14and the ID imprinter18are separately provided. These elements may be integrated into one element to thereby allow simultaneous execution of image restoration and ID imprinting.

Seventh, in the embodiment shown inFIG. 3, the program for decrypting and/or decoding is included in a viewer or a browser. The program may take any other form as long as it can restore the content into a suitable format for use by the user.

Eighth, although the ID information for one user is represented by one point in the frequency domain (FIG.6), the ID information may be represented in other forms. For instance, a set of a plurality of discrete points or a two dimensional region may be employed to represent the ID information for one user.

Ninth, in a frequency domain representation such as that shown inFIG. 6, reference information such as two straight lines100,102shown inFIG. 9may be added. This reference information can be utilized when reading the imprinted ID information from a content since its position is fixed and known in the frequency domain. By the help of the reference information, the location of the ID can be specified with more certainty to thereby identify the user represented by that ID even when the content has been modified through, e.g., rotation or enlargement.

Methods for imprinting ID information have been described. Methods for reading imprinted ID information will be described next.

If a content is illegally reproduced or modified (hereinafter referred to as an illegal action), it is desired that the unauthorized offender be identified. This can be achieved by reading the ID information imprinted into the content. A device for reading imprinted ID information (hereinafter referred to as a detector) may be provided anywhere in a network. A proxy server, for instance, may be equipped with such a detector.

FIG. 10is a flowchart showing the operation of a detector. The detector loads a content from a storage device or a memory medium (S10), and reads the ID information imprinted therein (S12). If an illegal action is detected, the detector resorts to appropriate measures, such as notifying a content manager of the unauthorized offender.

FIG. 11is a diagram showing an embodiment of the detector for reading ID information imprinted in a content. The detector60, which may be in a PC, comprises a communication section62for obtaining a content from a network, an ID reader64for reading the ID from the obtained content, and a display controller66for controlling a display68so as to display the read ID.

In this embodiment, the ID reader64extracts information from a predetermined location, for instance, the LSBs at a leading part of a data sequence of the obtained content, and reconstructs the ID based on the extracted data. If this process does not result in any ID information that meaningfully identifies a user, then the content is judged to be original, i.e., having no user ID information imprinted. On the other hand, if a content with a user's ID imprinted therein is found on a network, the user identified by the imprinted ID may have illegally distributed the content. Based on the ID, the possible illegal action is traced.

FIG. 12is a diagram showing an alternative ID reader according to another embodiment of the present invention. This ID reader operates to read an ID imprinted as spatial frequency information in a content. The ID reader64comprises an LSB extractor72for extracting the LSBs from the obtained content to form a bit pattern, and a FFT section74for performing fast Fourier transform (FFT) on the bit pattern formed by the extracted LSBs.

The operation here is a reverse operation of that shown inFIGS. 6to8. The LSBs, which represent the imprinted ID information, are first extracted (FIG.8). The bit pattern formed by the LSBs in the content is then detected (FIG.7). Spatial frequencies of the bit pattern in the x and y directions, respectively, are calculated by the FFT section74from the bit pattern. In the sample bit pattern shown inFIG. 7, the FFT calculation reveals user A's ID shown in FIG.6. The offender is thereby identified as user A.

This method is advantageous in that it does not require comparing the suspect content and the original content in order to detect the ID.

The above-described methods for reading imprinted ID information may have many5variations. Each variation of the ID imprinting method described earlier in this specification may have a corresponding variation of the ID reading method. For example, the ID can be read in cases where an offset has been added to a lower bit using a method such as the one described earlier with reference toFIGS. 13-16. Further, when an ID is imprinted in a predetermined location of the content, such as a location where shifts in data values do not produce significant perceivable effects, the readout method is provided to detect the same location consistent with the ID imprinting method. Generally speaking, ID reading can be done as long as the imprinter and the reader adopt the same imprinting/readout scheme.

In addition, although the detector is connected to a network in the above embodiments, it may be an off-line, stand alone type if it checks only contents stored in storage media.

Moreover, in the described embodiments, the ID imprinting is carried out at the information terminals where the content is used, i.e. at the user end. It will be apparent to a skilled artisan, however, that the various methods described herein for imprinting ID information in a content are equally applicable to a content distribution scheme in which ID imprinting is carried out at the content provider end.

It will, of course, be understood that modifications of the present invention, in its various aspects, will be apparent to those skilled in the art. Other embodiments are also possible, their specific designs depending upon the particular application. Therefore, the scope of the invention should not be limited by the particular embodiments herein described but should be defined only by the appended claims.