Improving DFT Watermarking robustness through optimum detection and synchronisation

In this paper, a new watermarking system for copyright protection of digital images is presented. The method operates in the frequency domain, by embedding a pseudorandom sequence of real numbers in a selected set of DFT coefficients of the image. Moreover, a synchronisation pattern is introduced into the watermarked image, to cope with geometrical attacks. After embedding, the watermark is hidden by exploiting the masking characteristics of the Human Visual System. An optimum criterion to verify if a given code is present is derived based on statistical decision theory, allowing a robust watermark detection without resorting to the original uncorrupted image.