Scaling detection method for watermarked MPEG content

In this paper, a method that provides robustness against scaling for watermarked MPEG content is described. We focus on a watermarking method that uses a pseudo-random sequence of block patterns and a tiled structure. Detection of the watermark information is based on a cross-correlation between the watermarked content and the watermark pattern. To make the watermark robust against scaling, the change needs to be detected, and it is applied to the detecting watermark pattern. Basically the scaling change is detected by observing the auto-correlation peaks generated by the tiled structure. However, for compressed domain watermark detection, a more sophisticated procedure is required, where an image is divided into 8 × 8-pixel blocks and transformed into DCT domain. We have developed a new correlation method, which only requires block-wise inner product calculations in DCT domain before correlation calculations are taking place. Then the correlation calculations are done in the complex domain and the phase of the peak correlation allows for precise scaling parameter detection. Since the cross-correlation for watermark detection is also done in the DCT domain, the proposed method has the advantages of easy implementation and detection performance.