Optimal watermark detection on interpolated images under noise

In this paper, the case where a low-resolution image is initially watermarked and the watermark is afterwards detected on a noisy interpolated version of the watermarked image is investigated, using a correlation detector. Polyphase decomposition is utilized at the detector side in order to enable the flexible formation of a fused image, which is appropriate for watermark detection. The optimal fused correlator, obtained by combining information from different image components, is derived through a statistical analysis of the correlation detector properties and employment of Lagrange multipliers. It is shown that it is always preferable to perform detection on a fused image rather than the original image. Experimental results establish the efficiency of the proposed scheme.