The proliferation of video images, especially over the Internet, is creating a need for a secure system that can allow a content provider to identify the source of any material. Such information could then be used for purposes of authentication of copyright ownership, copy control and management.
Recently, developers at the NEC Research Laboratory in Princeton, NJ, have patented a method to do just that.
Simply put, it works by digital watermarking many sorts of data types including image, video and multimedia data. Specifically, it inserts, detects and extracts embedded signals into subregions of the data.
Methods of watermarking images or image data require that the DCT (Discrete Cosine Transform) and its inverse of the entire image be computed.
Although there are fast algorithms for computing the DCT, when the image size is high, the computational requirement is also high, particularly if the encoding and extracting processes must occur at video rates, i.e., at 30 frames per second. Indeed, this method requires approximately 30 times the computation needed for MPEG-II decompression.
One possible way to achieve real-time video watermarking is to only watermark every Nth frame. However, many content owners wish to protect each and every video frame. Moreover, if it is known which frames contain embedded signals, it is simple to remove those frames with no noticeable degradation in the video signal.
An alternative option proposed by the NEC researchers is to insert the watermark only into subimages of the image. In that way, it is possible to tightly couple the watermark insertion and extraction procedures to those of the MPEG compression and decompression algorithms.
Considerable computational saving can then be achieved since the most expensive computations relate to the calculation of the DCT and its inverse and these steps are already computed as part of the compression and decompression algorithm.
The incremental cost of watermarking is then very small, typically less than five percent of the computational requirements associated with MPEG.