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. Index Terms-Attacks on digital watermarks, copyright protection, counterfeit watermarks, cryptography, invertible and noninvertible watermarking, invisible watermarks, quasi-invertible watermarking. I. INTRODUCTION T HE rapid growth of digital imagery coupled with the ease by which digital information can be duplicated and distributed has led to the need for effective copyright protection tools. Various watermarking schemes and software products have been recently introduced in attempt to address this growing concern. Given the flurry of activity that has resulted, it is natural to ask a few questions regarding all these efforts:

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Digital video archives are likely to be accessible on distributed networks which means that the data are subject to network congestion and bandwidth constraints. To enable new applications and services of digital video, it is not only important to develop tools to analyze and browse video, view query results, and formulate better searches, but also to deliver the essence of the material in compact forms.Video visualization describes the joint process of analyzing video and the subsequent derivation of representative visual presentation of the essence of the content. In this paper, we propose techniques to analyze video and build a compact pictorial summary for visual presentation. A video sequence is thus condensed into a few images-each summarizing the dramatic incident taking place in a meaningful segment of the video. In particular, we present techniques to differentiate the dominance of the content in subdivisions of the segment based on analysis results, select a graphic layout pattern according to the relative dominances, and create a set of video posters, each of which is a compact, visually pleasant, and intuitive representation of the story content. The collection of video posters arranged in temporal order then forms a pictorial summary of the sequence to tell the underlying story. The techniques and compact presentations proposed offer valuable tools for new applications and services of digital video including video browsing, query, search, and retrieval in the digital libraries and over the Internet.Index Terms-Browsing, compact representation of video, digital library applications, Internet, pictorial summary, video analysis, video database, video visualization.

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