The need to safeguard the property rights of multimedia content from unauthorized copying and the possibility to determine the true owners of the asset can be faced by resorting to efficient digital watermarking systems. This chapter presents a mathematical formulation to define a digital watermarking system and describes the general requirements to be satisfied, with more emphasis given to the aspects of security, robustness, and imperceptibility. After this general discussion, the two main classes of digital watermarking schemes, namely the spread-spectrum watermarking and the side-informed watermarking are explained by highlighting their main advantages and drawbacks. This analysis is completed by the description of a practical implementation of a digital image watermarking scheme. Finally, the use of watermarking systems in the framework of a DRM is deeply analyzed.
Mathematical Formulation Of The Watermarking Problem
A digital watermarking system can be modelled as described in Figure 1 (Barni, 2004). The inputs of the system are a certain application dependent information, and the original host content, that could be an audio file, an image or a video sequence, here indicated as C. The to-be-hidden information is usually represented as a binary string b= (b1,b2,….,bk), referred as the watermark code. The watermark embedder hides the watermark code b into the host asset C to produce a watermarked content Cw, usually making use of a secret information K needed to tune some parameters of the embedding process and to allow the recovery of the watermark only to authorized users having access to that secret information.
The proposed model describing a digital watermarking system