Detection-theoretic analysis of warping attacks in spread-spectrum watermarking

This paper studies the effects of desynchronization attacks such as delay and warping on the performance of blind spread-spectrum watermark detection systems. The host signal is modeled as a colored Gaussian signal. Evaluation of the optimal likelihood ratio test is often computationally expensive, so as a practical alternative, we propose a family of quadratic detectors and construct the detector and family of watermarks that maximize the deflection criterion. Experiments are carried out to verify the suitability of the deflection as a performance index. Substantial improvements over conventional watermark designs are demonstrated.