LMS-based attack on watermark public detectors

We describe a generalized attack on image watermarking schemes when the decoder is publicly available. The attack applies to most common watermarking schemes. In particular, we describe in detail the implementation of the attack against correlator-based watermark detectors using the least mean square (LMS) algorithm. We establish the effectiveness of the attack in removing the watermark with least distortion. Also, we describe a counterattack to avoid this problem by using nonparametric decision boundaries at the detector.