Image analysis – Applications
Reexamination Certificate
1998-06-08
2001-09-04
Johns, Andrew W. (Department: 2621)
Image analysis
Applications
C380S202000
Reexamination Certificate
active
06285774
ABSTRACT:
TECHNICAL FIELD
This invention relates generally to copy protection for data obtained from any source, such as information-bearing media, (e.g., DVD's), and more particularly to data modification to help enable an unauthorized copyist to be identified.
BACKGROUND ART
Consumer devices for recording and playback of recorded program material, such as movies, software and the like, are widely available. Media bearing such material include magnetic tape, recorded and played back using a VCR, and now more recently optical media such as CDs, CD-ROM's and DVD's. The DVD is new optical disk technology, capable of holding enough information typically for a 133 minute movie on each layer. The DVD often uses a so-called MPEG-2 data compression standard that enables video material to be efficiently stored and reproduced without significant visible degradation. Other standards for video and other types of information, such as embodied in software, can be utilized.
The cost of producing program material, such as entertainment movies, is considerable, whereas, the cost to the copyist is relatively low. Hence, movie piracy has become a substantial source of loss of revenue for the movie industry. Indeed, more than 2 billion dollars are lost to copyists annually, mainly in the form of bootleg video cassettes. DVD may make the situation even worse, as the audio and video programming from a DVD player have high fidelity and considerably more information content than that possible from VHS.
Two approaches to thwarting piracy have been implemented by legitimate producers of movies and other types of material having commercial value, such as software: (1) injecting, into a protected medium, a signal that distorts the material in some manner when played, and (2) watermarking, by injecting a visible or invisible static symbol or mark that identifies the source of the original material.
Watermarking commonly is performed on a medium at the point of authoring of protected material. An example is at a post house or other facility at which the information-bearing medium is produced. However, once recorded, the watermark is fixed. Although the watermark will identify the source of authoring of the material, it will provide no information on the identity of an unauthorized copyist. The identity of the copyist must be obtained from information gathered at the point of playback and copying. This may include such information as identification of the equipment used by the copyist and time of copying. Circuitry to provide this information at the playback unit, however, will increase the cost of the unit, a considerable disadvantage in this competitive industry. An objective of this invention is to produce a tracing signal at the point of use, that varies in dependence of, and is unique to, the copyist of a protected medium. Another objective is to do so without adding significant cost to the playback unit. An objective further is to carry this function out in digital or analog space, depending on the domain of the medium.
The protective signal furthermore must be unpredictable, as predictability will enable a copyist either to filter out the signal, or alter it so as to provide a false designation of source. The protective system further must be robust, as any source of copying message injected into the signal stream must be recovered in an environment having heavy transmission noise, and unintentional or intentional distortion. Furthermore, the sending message must be difficult to detect, modify or remove. The message content should be protected and difficult to decode, even if the transmitted bits identifying source are available. Finally, the output stream must be legal to enable proper decoding in the appropriate domain. An additional objective of this invention is to produce a point of use signal, injected into the signal stream of the protected medium, that is difficult for a copyist to detect or alter. The point of use signal furthermore should be able to be injected into any type of protected content, including audio and software, in addition to video.
DISCLOSURE OF INVENTION
In accordance with the invention, a method of processing an information-bearing compressed digital signal stream is performed to modify the stream by adding a “source-of-copying message” in the form of “running marks” distributed among pixel blocks or macroblocks of video frames, to enable tracing to the source of an unauthorized copy. The modified signal stream, in normal use, is sent to a television display or a monitor for viewing by a user. The running marks are subtle and generally invisible. However, if the signal stream is used to make an unauthorized recording, the recording will bear the original compressed digital stream together with a source-of-copying message. Hence, by comparing the original digital signal stream with the modified signal stream, the message can be extracted, to trace to the copyist.
In the preferred embodiment, by way of example, the compressed digital signal stream is an audio/video data stream encoded in an MPEG standard. Pixel blocks or macroblocks are selected on a frame basis as candidate regions, termed “message holes,” for carrying the source of copying message. The message holes correspond to a selected segment of the MPEG bitstream relating to a block or macroblock of a picture frame which can be changed for bit modulation.
The source-of-copying message is applied to the signal stream as replacement bits during playback of the prerecorded material (such as a movie). Bit modulation of the macroblocks selected to be message holes may be performed in various ways. In the preferred embodiment, by way of example, modulation is carried out by adding or subtracting a prescribed amount of noise to or from the selected macroblock, preferably in the (DCT) discrete cosine transform domain (but alternatively in the video domain). This has the advantage of spreading out distortion within the macroblock and making pixel distortion difficult to see.
The message holes may be located in frames randomly, but preferably are selected to reside at textured portions of the image, such as at an image boundary, that will accommodate an alteration invisibly or nearly so to the user. Candidate message hole locations may be selected, for example, frame by frame (but alternatively by multiple frames at one time), by operator input or machine implementation. The selected locations then may be redistributed to form a more uniform distribution of message holes among frames. Redistribution may be based on maintaining the number of message holes to be close to a target number of message holes per frame, while avoiding clustering within any single frame or among a small number of neighboring frames.
To maintain the number of bits contained in selected macroblocks within a row relatively constant, after running marks are added, the number of bits may be compensated by MPEG re-encoding to conform to the MPEG standard and avoid buffer underflow or overflow. This may be done, for example, by varying the quantization scaling factor of macroblock pixels until the original number of macroblock bits and the bit count after encoding with running marks are approximately equal.
Following selection of message hole candidates, and during the re-encoding process, the candidate message holes are tested to determine whether they satisfy prescribed criteria and should be used for inserting source of copying message bits, and either are accepted, discarded or redistributed Examples of unsuitable or potentially unsuitable message holes include: message holes in a row that lie on a DVD sector boundary, message holes in a row that cannot be re-encoded for bit compensation, message holes that contain message bits that cannot be reliably decoded and message holes that are to be skipped following re-encoding.
The source-of-copying message may correspond to one or more of the following: serial number of the authorized playback unit from which the unauthorized copy is made, serial number of the medium copied, and time of copying. This i
Bergeron Michael
Bugwadia Kobad
Ehrhardt Jack
Iu Siu-Leong
Mercier Guillaume
Digital Video Express, L.P.
Johns Andrew W.
McDermott & Will & Emery
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