Dual Protection of JPEG Images Based on Informed Embedding and Two-stage Watermark Extraction Techniques

摘要

A watermarking scheme, proposed to embed both image-dependent and fixed-part marks for dual protection (content authentication and copyright claim) of JPEG images, is described in this paper. To achieve the goals of efficiency, imperceptibility, and robustness, a compressed-domain informed embedding algorithm, which adopts Lagrangian multiplier optimization approach followed by an iterative refinement procedure, is developed. To robustly detect the fixed-part watermark, a two-stage watermark extraction procedure is devised. At the first stage, the semi-fragile watermark in each channel is extracted for content authentication. At the second stage, a weighted soft-decision decoder, in which the signal detected in each channel is weighted according to the estimated channel condition, is used to raise the recovery rate of the fixed-part watermark for copyright protection. Experimental results manifest that the proposed scheme can not only achieve the purposes of content authentication (semi-fragile watermarks to resist mild image alterations and detect malicious tampered regions) and copyright protection (robust watermarks to claim the ownership), but also maintain higher visual quality (by at least 4 dB than the prior method) at a specified watermark robustness.