Scalar DC–QIM for Semifragile Authentication

Semifragile watermarking can be used to detect illegal and local manipulation, while being robust toward legal processings such as lossy compression. The aim of this work is twofold: 1) we first formalize this semifragile authentication problem by proposing an appropriate payoff: by considering the watermark as an integrity stamp (i.e., its detectability stands as an integrity evidence), a natural game cost is the false-alarm probability which still detects the watermark in a tampered content and 2) this approach is further applied to find the optimal power allocation across parallel additive Gaussian channels of a dithered distortion compensated scalar quantization-based scheme against substitution attacks. The results are specialized to design an efficient discrete cosine transform (DCT) semifragile image watermarking system which allows detecting substitution attacks despite JPEG compression.