The authors’ introduction to this well-written article states that, “thanks to the proliferation of the World Wide Web, a huge amount of multimedia content--text, graphics, images, video and audio--are available for browsing and downloading by millions of users worldwide over the network. As a result, security and copyright issues have become important problems in research and applications. Digital watermarking is applicable in copyright protection, ownership assertion, and integrity checks in multimedia content.”

Digital watermarking, like analog watermarking, adds a background pattern to a digital image. The authors probably should have restricted their statements to images rather than encompassing multimedia, because watermarking audio would be somewhat perplexing to a listener and watermarking video would seem like overkill. Nevertheless, they have produced a definitive paper on digital watermarking. It has been done in the scholarly way typical of Communications of the ACM: it is carefully edited and beautifully laid out, with appropriate color and black-and-white illustrations. The references also seem to be appropriate and adequate.

A short history of watermarking should have been included. Instead, the authors assume that readers are familiar with such protective and decorative techniques. Additionally, they either omit or give short shrift to alternative protective techniques. In particular, it is common for online art dealers to degrade the quality of images of their products to a common PC monitor resolution in order to discourage illegal copying that would replace buying a quality print from the dealer.

The authors freely admit that, regardless of how an image may be digitally watermarked, “no known technique can survive a resourceful and clever attacker.” They also predict “many new watermarking approaches and applications in the near future.” We shall see. Anyone interested in Internet commerce protections would do well to read this paper.