Digital watermarks have been proposed in recent literature as a means for copyright protection of multimedia data, In this paper we address the capability of invisible watermarking schemes to resolve copyright ownership. We show that, in certain applications, rightful ownership cannot be resolved by current watermarking schemes alone. Specifically, we attack existing techniques by providing counterfeit watermarking schemes that can be performed on a watermarked image to allow multiple claims of rightful ownership. In the absence of standardization and specific requirements imposed on watermarking procedures, anyone can claim ownership of any watermarked image. In order to protect against the counterfeiting techniques that we develop, we examine the properties necessary for resolving ownership via invisible watermarking, We introduce and study invertibility and quasi-invertibility of invisible watermarking techniques, We propose noninvertible watermarking schemes, and subsequently give examples of techniques that we believe to be nonquasi-invertible and hence invulnerable against more sophisticated attacks proposed in the paper. The attacks and results presented in the paper, and the remedies proposed, further imply that we have to carefully reevaluate the current approaches and techniques in invisible watermarking of digital images based on application domains, and rethink the promises, applications and implications of such digital means of copyright protection.
