Abstract:
Fingerprinting and fingerprint detection, techniques are described which, unlike typical fingerprint systems used to conceal video signals, are compatible with all conceivable forms of signal compression systems while still allowing viewing of the video signal. The fingerprint technique is based on the principle of applying very slight local spatial distortion to the pixels in a video image, and the like, by means of selected warp patterns. Thus the technique provides means for conveying, within the video signal, selected information in the form of the fingerprint which is detectable electronically but which is not noticeable to a critical viewer who is watching the video signal. That is, the resultant fingerprinted video signal will appear to be identical to the undistorted video signal. the fingerprint detection technique provides for the recovery of the conveyed information which may comprise an instruction to prevent the fingerprinted video image from being copied, messages which allow identifying the source and date of an unauthorized copy of the video image, etc.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is related to U.S. Pat. No. 5,659,613 (&#39;613) issued Aug. 1997 entitled Method and Apparatus for Copy Protection for Various Recording Media Using a Video Finger Print, by John O. Ryan and Gregory C. Copeland, to U.S. Pat. No. 5,513,260 (&#39;260) issued Apr. 30, 1996 entitled Method and Apparatus for Copy Protection for Various Recording Media, by John O. Ryan, and to U.S. Pat. No. 5,739,864 (&#39;864) issued Apr. 14, 1998, entitled A Video Finger Print Method and Apparatus, by Gregory C. Copeland. This application also is related to copending patent application Ser. No. 09/171,856, filed May 29, 1997; entitled Method and Apparatus for Compression Compatible Video Scrambling, by John O. Ryan. 
    
    
     BACKGROUND OF THE INVENTION 
     There are two prior patent applications of mention above which discuss video fingerprint methods for video signals. The &#39;864 application by G. C. Copeland discloses a video fingerprint method that inserts a low frequency low level signal within the video signal, such that is not observable to the viewer, but is readily detectable by a special detection circuit. This low level signal operates over many fields in a manner that makes it possible to detect and identify the source of the signal. The disadvantage of &#39;864 prior art is that the fingerprint method may not be compatible with certain video compression systems. The &#39;613 application by J. O. Ryan and G. C. Copeland uses the concepts of the &#39;260 patent application for a scrambling system for various recording media. 
     EPO Application 0 690 595 describes a method and apparatus that encodes identification information into a stream of digital data representing an object. The digital data representing an object is modified to add embedded identification information into the data. This modification is done such that the resultant changes to the object are not objectionable to the user. By comparing the original data to the modified data, the possessor of the original data can recover the embedded identification information. However the identification information is effectively unavailable to anyone not possessing the original data. 
     There is a need for a secure video fingerprint method having the property that the fingerprinted video be compatible with the various video compression systems currently in use. In particular, it should be compatible with compression systems based on for example the Discrete Cosine Transform (DCT), which may employ inter-field redundance coding. Motion picture experts group (MPEG-1 and MPEG-2) are examples of such compression systems. In anticipated applications, the video signal generally is subjected to the processes of fingerprinting, compression, decompression and fingerprint detection—in that order. The fingerprinted video therefore will be subjected to the processes of compression and decompression prior to fingerprint detection. 
     The fingerprint systems of previous mention may tend to disturb the inter-field redundancy in a television signal that the compression systems of previous mention depend upon for proper operation. When the inter-field redundancy is disturbed, the bit rate requirements for the compression system rise, possibly to an unacceptable level, for the transmission path of the compressed video signal. Therefore there is need for a fingerprint system that does not degrade the inter-field redundancy to a level that requires excessive bit rates to provide a given picture quality. 
     SUMMARY OF THE INVENTION 
     The present invention provides a fingerprint method and apparatus which overcomes the compression system incompatibility of the prior art fingerprint systems of previous mention, while further meeting other various desirable requirements such as not being observable to a viewer while conveying information in the active video signal. 
     In addition, the present invention meets requirements such as the following: 
     Video Standards 
     The fingerprint method and apparatus of the invention is applicable to either analog (NTSC, PAL, SECAM) or digital (CCIR-601) video signals. 
     Security 
     The present fingerprint method and apparatus intrinsically provides a high level of resistance to hacking. In other words, it is very difficult to remove the fingerprint from the video. 
     Invisibility 
     The present fingerprint method and apparatus primarily is intended to convey information in entertainment applications such as video movies, television (TV) shows, and the like. It is essential that the fingerprint method not affect the entertainment value of the video image while being securely concealed within the image, but must be readily detectable by, for example, a detection circuit in a disk or tape recorder or other signal processing apparatus. 
     General Video System Compatibility 
     In addition to the foregoing requirements and attendant advantages, for maximum operational flexibility, the invention ensures that the fingerprinted video signal appears as a normal video signal to most if not all video processing methods and devices designed to operate with unfingerprinted video signals, and the like. 
     In particular, the video signal&#39;s fingerprinted in accordance with the invention is compatible with all video recording, transmitting and processing devices likely to exist in a production or editing environment. Passage of the fingerprinted video through these devices does not cause the fingerprint to be removed or be made more difficult to detect. 
     Further, the present fingerprint method and apparatus, or at least a particular embodiment thereof, is compatible with consumer video cassette recorders (VCRs). That is, the invention makes it possible to record the fingerprinted video signal on a consumer grade VCR, and replay it later for detection without any likelihood of it being removed during the record/replay process. 
     More particularly, the invention provides a library of warp patterns, each of which is capable of imparting a selected degree of local spatial distortion to a video image. In response to an operator&#39;s selection, a pattern select code determines which stored warp pattern is supplied as a fingerprint signal to a warp engine. The warp engine in turn applies the selected warp pattern to the video image to correspondingly locally spatially distort the image. The slight distortion imparted by the selected warp pattern is not observable to a viewer, but is detectable by a circuit in a recording device to, for example, prevent the recording device from copying the video signal. Alternatively, the fingerprint also allows subsequently comparing the original unfingerprinted video signal and an unauthorized copy of the fingerprinted video signal, to determine the origin, date, etc., of the unauthorized copy. For example, in the event a fingerprinted video signal is illegally recorded onto a disk or tape, the spatial distortion imparted by the fingerprint technique remains with the recorded video image. Thus a subsequent comparison between the pixel positions of a fingerprinted signal (that is, an illegal copy) and the unfingerprinted original signal, can be used to identify the source of the illegal copy. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a photograph of an image in which a fingerprint has not been applied by the invention; 
     FIG. 2 is a photograph of an image in which a fingerprint has been applied in accordance with the invention; 
     FIG. 3 is a block diagram illustrating an embodiment of a fingerprint apparatus in accordance with the invention; and 
     FIG. 4 is a block diagram illustrating an embodiment of a fingerprint detection apparatus in accordance with the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention provides a method and apparatus for fingerprinting, via a signal fingerprinting technique, various program distribution media such as digital video disk (DVD) or digital video cassette recorder (DVCR), as well as broadcast and cable video distribution channels. 
     A compression system such as, for example, MPEG 1 and 2 of previous mention, relies on the condition that a high degree of redundancy exists in the image, both intra-field and inter-field redundancy. 
     The invention employs the same basic spatial image distortion concept as disclosed in the above-mentioned related application entitled Method and Apparatus for Compression Compatible Video Scrambling, by J. O. Ryan. However, the present invention applies a much smaller distortion which can still be detected by a suitable circuit and which will not be noticeable to a viewer. 
     The explanation of the invention method and apparatus is facilitated by the following analogy. Consider a scene viewed through a sheet of colorless transparent glass with a slightly bumpy surface. By specifying very slight“bumpiness” parameters, the resultant image will appear to be identical to the undistorted image, although the positions of the specific pixels in the image are slightly shifted relative to their normal positions. In effect, the applied fingerprint does not distort the image visibly, but the small distortion may still be readily detectable by a suitable detector circuit. For example, a recorder having this fingerprint detector circuit could be prevented from copying the fingerprinted video signal. Thus, in effect the fingerprint added to the video signal is a means for conveying a message or instruction which, in the above example, instructs the recorder to not copy the video signal. Alternatively, in the event that an illegal copy of the fingerprinted video signal is found, the message conveyed can be used to identify the source of the illicit copy, the date of recording, or other information. 
     Although the present invention conveys information within the video signal, the fingerprint technique is compatible with all conceivable forms of compression systems because the application of the fingerprint does not materially increase the information content of the video signal. The various pixels may be very slightly closer or further from each other in any direction. Thus it follows that the high frequency content or detail is very slightly increased and decreased in various areas of the image, but there is no noticeable change in the bit rate of the compressed (or uncompressed) signal. 
     Thus, the technique of the invention is based upon a“local spatial distortion” of the active video signal. More particularly, the invention comprises a particular kind of optical image scrambling which when modeled in the video domain becomes the basis of a video fingerprint system having all of the desirable properties and requirements, and thus the attendant advantages, of previous mention. 
     To this end, a video processing means for providing the fingerprint method and apparatus of the invention, embodies a slight local spatial image distortion of a video signal which is not visually noticeable and which is electronically detectable. Such a device is referred to herein as a spatial image distortion (SID) fingerprint inserter having the following properties: 
     displacement of each pixel of the original image by a slight amount unnoticeable to the eye (which may be zero) horizontally and/or vertically. 
     maintaining a given pixel in the fingerprinted image with the same set of contiguous pixels that it had in the original image. 
     An array of number pairs, one pair for each pixel, is needed to describe the fingerprint signal for each field. The field fingerprint signal, herein termed a“warp” pattern for ease of description, may be arranged to remain fixed for relativity long periods, to change slowly with time, or to change from field to field. By appropriate choice of warp patterns and by limitation of their range so as to be detectable electronically but not visually noticeable, it is possible to effect a fingerprint system having all of the properties and requirements specified above. 
     There are an infinite number of warp patterns available each of which designates the amount of displacement horizontally and vertically of each pixel in the image. The warp pattern can be fixed for an entire movie or vary throughout the movie. 
     In one application of the invention the warp pattern remains unchanged throughout the entire movie or program, and that particular pattern may designate a particular copy, or the broadcast time and source, of the program for broadcast application. If illicit copies of the program are discovered later, these copies may be compared with the original unwarped program in a suitable correlating device which identifies the specific warp pattern used, to thereby identify the source of the illicit copy. 
     For this application, the warp pattern can be“morphed” from one pattern to another, or can be faded to zero warp and back again, preferably gradually over a selected time interval such as a number of frames up to a longer time interval of a plurality of seconds. The purpose for applying changing warp patterns is to increase the level of security, that is, to make it even more difficult for unauthorized persons to discover the identify of the warp pattern and thus override the fingerprint process. 
     In another application the teachings of the present invention may be used to convey FIG. 3 illustrates an embodiment of a fingerprint apparatus of the invention herein referred to as a fingerprint inserter  10 . A digital video signal or the like is supplied to a field/frame store  14  via an input lead  12 . The field/frame store  14  provides means to store a field or frame of video and to supply the video to a first input of a warp engine  16 . In response to a user selection, a warp pattern select code generator  18  generates a warp pattern select code which, in turn, selects a desired warp pattern from a warp pattern library  20  which may include for example a look up table. The selected warp pattern is supplied as a fingerprint signal to a second input of the warp engine  16 . The warp pattern is applied by the warp engine to distort accordingly the pixel positions in the appropriate lines of the field or frame of video from the field/frame store  14 . The output of the wrap engine  16  consists of the fingerprinted video signal which is supplied to a pattern select code inserter circuit  22 . Circuit  22  inserts a code identifying the selected pattern into the fingerprinted video signal, which then is coupled via an output lead  24  to any downstream digital processing circuits and/or devices used in the associated video processing application. 
     For example, a particular SID pattern may be used which generates a slight vertical nonlinearity in the scene, such that while the center of the image is held fixed, the top and bottom regions are caused to meander vertically about their proper locations at a predetermined rate. The amount of the displacement may be a fraction of a percent of picture height so as to be invisible, and the rate of change may be, say, one cycle per second. instructions to a device such as, for example, a video recording device. 
     FIG. 3 illustrates an embodiment of a fingerprint apparatus of the invention herein referred to as a fingerprint inserter  10 . A digital video signal or the like is supplied to a field/frame store  14  via an input lead  12 . The field/frame store  14  provides means to store a field or frame of video and to supply the video to a first input of a warp engine  16 . In response to a user selection, a warp pattern select code generator  18  generates a warp pattern select code which, in turn, selects a desired warp pattern from a warp pattern library  20  which may include for example a look up table. The selected warp pattern is supplied as a fingerprint signal to a second input of the warp engine  16 . The warp pattern is applied by the warp engine to distort accordingly the pixel positions in the appropriate lines of the field or frame of video from the field/frame store  14 . For example, a particular SID pattern may be used which generates a slight vertical monlinearity in the scene, such that while the ccenter of the image is held fixed, the top and bottom regions are caused to meander vertically about their proper locations at a predetermined rete. The amount of the displacement may by a fraction a percent of picture height so as to be invisible, and the rate of change may be, say, one cycle per second. 
     FIGS. 1 and 2 illustrate an original picture or video image without a fingerprint and a video image with the addition of a fingerprint, respectively, in accordance with the present invention. As may be seen in FIG. 2, the application of a warp pattern does not cause a visually noticeable distortion in the image. 
     A suitable detector may be constructed as shown in FIG.  4 . Firstly, in order to minimize the effect of normal scene movements, a motion detector  30  examines the edges and the center region of the image for movement and applies a compensating correction via a motion corrector  32  to the video, which then is fed to a SID detector  34 . In the event that large changes are detected, the measurement process is temporarily halted. This makes it easier for the SID detector to detect the SID pattern in the presence of normal scene motion. The motion-compensated video is thus subjected to motion detection in only those regions affected by the SID pattern, in this case regions near the top and bottom of the image. The resulting motion vectors are examined in a comparator  36  for correspondence both in magnitude and time with reference vectors expected for the particular SID pattern used, and if a correspondence is found the “fingerprint” has been detected. 
     For example, a particular SID pattern may be used which generates a slight vertical nonlinearity in the scene, such that while the center of the image is held fixed, the top and bottom regions are caused to meander vertically about their proper locations at a predetermined rate. The amount of the displacement may be a fraction of a percent of picture height so as to be invisible, and the rate of change may be, say, one cycle per second. 
     A suitable detector may be constructed as shown in FIG.  4 . Firstly, in order to minimize the effect of normal scene movements, a motion detector examines the edges and the center region of the image for movement and applies a compensating correction to the video fed to the SID detector. In the event that large changes are detected, the measurement process is temporarily halted. This makes it easier for the SID detector to detect the SID pattern in the presence of normal scene motion. The motion-compensated video is then subjected to motion detection in only those regions affected by the SID pattern, in this case regions near the top and bottom of the image. The resulting motion vectors are examined for correspondence both in magnitude and time with the vectors expected for the particular SID pattern used, and if a correspondence is found the “fingerprint” has been detected. 
     In one this embodiment, the fact that the video has undergone spatial image distortion according to some pre-arranged pattern and/or timetable is used to indicate the source of an illicit copy. The various sources or prints of the original video are subjected to different SID patterns which uniquely identify the source or the print. At a later time, if an illicit copy of the program surfaces, it will be possible to identify the source or print from which this copy was made. 
     To do this, the original video (from an archive) is compared with the illicit copy. The two video signals are first frame-synchronized and the signal levels are adjusted to be equal. Any horizontal or vertical offsets between the two images are also corrected for using simple subtraction techniques to show up difference. 
     In one embodiment of the invention, the SID may be applied only to specific segments of the video program. In another embodiment, a specific SID pattern may be faded in and out according to a specific timetable. Or both embodiments may be combined to increase the possible permutations. In an example of the latter, a particular SID pattern may be used which generates a slight horizontal non-linearity in the scene, such that while both sides of the image remain fixed, the center meanders to the left and right of its proper location at a predetermined rate. Furthermore, only certain time segments of the program are subjected to this distortion. An operator viewing the subtracted images on a monitor can easily see this SID pattern, note the time segments when it occurs and its rate of change, and thereby identify the source of the illicit copy. Although the invention has been described herein relative to specific embodiments, various additional features and advantages will be apparent from the description and drawings. For example, the invention techniques may be applied to a medium other than video signals, such as, for example, photographs, computer generated images, etc. By way of example, the local spatial distortion technique can be used to identify the origin of illegal copies of proprietary photographs. To this end, as described above, a negative of a photograph may be electronically reproduced several times using a slightly different warp pattern each time by altering the scanning beam very slightly. Each resulting new negative thus contains a different fixed spatial distortion which can be detected subsequently in accordance with the invention as described above to identify the photograph and thus the source of any illegal copies thereof. 
     Thus the scope of the invention is defined by the following claims and their equivalents.