Digital Watermarking Robustness and Fragility Characteristics: New Modelling and Coding Influence Marcos de Castro Pacitti 1 and Weiler Alves Finamore 2 1 Brazilian Air Force, pacitti@cc.sivam.gov.br 2 CETUC/ PUC - Rio, Brazil weiler@cetuc.puc-rio.br Abstract. This paper, introduces a new methodology for the design and analysis of digital watermarking systems which, from an informa- tion theoretic point of view, incorporates robustness and fragility. The proposed methodology is developed by focusing on the probability of er- ror versus watermark-to-noise ratio curve, describing the technique per- formance, and a scenario for coded techniques which takes into account not only the coding gain, but also the robustness or fragility of the sys- tem. This new concept requires that coded digital watermarking systems design be revisited to also include the robustness and fragility require- ments. Turbo codes, which appropriately meet these requirements, can be used straightforwardly to construct robust watermarking systems. Fragile systems can also be constructed by introducing the idea of polar- ization scheme. This new idea has allowed the implementation of hybrid techniques achieving fragility and robustness with a single watermark embedding. We moreover, present (turbo) coded techniques which can also be used in a semi-fragile mode. 1 Introduction Watermarking refers to the process of embedding in a host information an infor- mation mark which is not immediately discernible upon examining the embedded host information. These techniques have been used as a way of reducing coun- terfeiting in documents, currency, and other applications for centuries. With the widespread use of digital representation of images, video, audio, and other sig- nals, the copyright protection by using an “invisible” digital watermarks became a very active area of research. Naturally many new watermarking applications have become of great interest in this new digital perspective, including national security applications such as integrity and authenticity verification, covert com- munication and traitor tracing (finger printing) applications. Several other digi- tal watermarking applications are still emerging, bringing a wide perspective for research [1]. Watermarking in this new context is a complex problem, with issues that involve not only the watermarking techniques themselves, but also system design,