Image analysis – Applications
Reexamination Certificate
1998-04-23
2002-03-19
Johns, Andrew W. (Department: 2721)
Image analysis
Applications
C382S248000
Reexamination Certificate
active
06359998
ABSTRACT:
BACKGROUND OF THE INVENTION
1. The Field of the Invention
The present invention generally relates to the field of digital imaging of multimedia data. More particularly, the invention relates to embedding a sufficiently robust watermark into the image data that can withstand lossy compression schemes without degrading the digital watermark.
2. Present State of the Art
The number of applications that use digital storage and transmission is increasing at a rapid rate. Specifically, types of digital data include digital audio, digital images and digital video, which may be largely electronically distributed over ubiquitous public networks such as cable and telephone infrastructures. Additionally, digital data may be physically exchanged and replicated into exact duplicates of the original.
The proliferation of digital media, e.g., audio, image and video, creates property concerns relating to intellectual property rights, e.g., copyrights. Traditional cryptographic techniques have provided one level of protection by allowing decryption of the encrypted data to be performed only by decryption key holders. However, conventional cryptography provides little protection against data piracy, i.e., unauthorized reproduction of decrypted digital data, since decrypted digital data may be easily replicated and distributed. Such schemes provide insufficient protection against unauthorized reproduction of information and the inability to determine the source or origin of unauthorized duplicates.
It is known in the prior art to provide a “digital watermark” on a document to address this problem. Traditional digital watermarks on a data file or document may be perceptible and even visible or may be sufficiently embedded within the digital data so as to be imperceptible to those perceiving the digital data. Such digital watermarks remain present within the data even after processing such as a decryption procedure. While visible or humanly perceivable digital watermarks may provide apparent identification of the incorporating entity, such as a copyright owner, noticeable digital watermarks are considered unacceptable for aesthetically integrous media, e.g., imaging and audio data.
Imperceptible watermarks are comprised of an identification code that is permanently embedded within the digital data and may contain specific information such as the identity of the purchaser of a particular copy of the digital data, e.g., audio (speech and music), images (photographic and graphics) and video (movies).
There are techniques that have been proposed for watermarking digital data. In U.S. Pat. No. 5,464,997 to Barton, a method and apparatus is disclosed for basic authentication of a digital block such as an image carrying authentication information provided by the user embedded into the digital block of data. A digital signature comprised of a reduced representation of the digital block of data is embedded by replacing predetermined bits within the digital block of data. The authentication process is performed in reverse order so as to expose the embedded digital signature, thereby authenticating the integrity of the digital block of data. It should be pointed out that such an implementation while adequate for digital data transmission and storage techniques that do not impose compression techniques, are wholly inoperative in modern communication channels that employ sophisticated modulation techniques and other lossy compression methods. While it is possible to employ techniques such as those that use the least significant bits (LSBs) of the image data to conceal or embed the digital watermark, such approaches are obviously not sufficiently robust for enduring lossy compression processes as lossy compression techniques tend to randomize the LSBs. Furthermore, employing the most significant bits of the data image renders the digital watermark perceptible and therefore unacceptable or undesirable for aesthetically demanding forms of digital data. Additionally, employing a frequency transformation followed by embedding the digital watermark in the high frequency bands is also insufficiently robust since elementary lowpass filtering results in the decimation of the digital watermark. Conversely, placing the digital watermark in the low frequency components causes the digital watermark to become perceptible and therefore aesthetically unacceptable. Therefore, it should be apparent that the objectives of creating an imperceptible digital watermark that is additionally sufficiently robust to lossy image processing, e.g,, compression and rescaling, are in direct conflict. That is to say, if the digital watermark is sufficiently robust to lossy imaging processing operations, the digital watermark becomes perceptually significant and therefore unacceptable. Conversely, embedding the digital watermark so as to be imperceptible results in an inadequately robust digital watermark.
It is known that orthogonal transforms e.g., Discreet Cosine Transform (DCT) and Discreet Fourier Transform (DFT), can be used to perform digital watermarking in the transform domain as taught in Cox et al.,
Secure Spread Spectrum Watermarking for Images, Audio and Video
, Proceedings of the 1996 International Conference on Image Processing, Vol. III, pp. 243-246, 1996. In that particular public description, the authors propose inserting a watermark into the spectral components of the digital data using techniques analogous to spread spectrum communications, i.e., hiding a narrow band signal in a wide band channel which is represented by the digital data. However, in such DCT-based approaches, spectral energy is concentrated which facilitates data compression, but becomes disastrous for retaining the integrity of the digital watermark.
In such DCT-based approaches, the low-frequency components are employed, but the mean-value coefficient is excluded. Such an implementation suggests that the DCT-based approaches are not systematic. Such approaches were studied and proposed by Cox et al. due to the popularity of DCT in the industry. Therefore, orthogonal transforms such as the DCT or the DFT are good choices for compression, but are less than desirable choices for digital watermarking. The fundamental disadvantage of such techniques result from the fact that such techniques offer energy compaction and are therefore not sufficiently adequate choices for a spread spectrum-based algorithm.
Thus, it appears that there exists no digital watermarking scheme that is capable of embedding an adequately imperceptible digital watermark into a digital data file, wherein the digital watermark is sufficiently robust to withstand lossy image processing operations (e.g., compression and resealing), while remaining detectable following such degradation processing. There also does not exist any digital watermarking technique that is sufficiently strongly resistant to unauthorized detection and decoding, even by individuals cognizant of the present watermarking techniques. Finally, there exists no digital watermarking technique that may be applied to all media types, e.g., audio, images, video, graphics and text (when represented as an image), that may be universally applied.
SUMMARY AND OBJECTS OF THE INVENTION
It is an object of the invention to provide a method for watermarking digital data in such a manner as to cause the digital watermark to remain resilient throughout lossy compression processes.
It is a further object of the present invention to provide a method for designating and determining the origin of digital data which may be subjected to lossy compression techniques through the use of a digital watermark.
It is a further object of the present invention to provide a method for spreading a digital watermark across digital data such that when a portion of the frequencies of the digital data are compressed and thereby disposed, the digital watermark remains intact and discernable.
Yet another object of the present invention is to provide a method for determining the origin of a particular copy of digital data through the use of a digital watermark ad
3Com Corporation
Alavi Amir
Johns Andrew W.
Workman & Nydegger & Seeley
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