Abstract: A semi-fragile watermarking scheme needs robustness to some common attacks and capability of checking tamper.The combination of DCT and DHT is analyzed.From the analysis,a novel semi-fragile watermarking scheme is presented.In this scheme,the host image is first transformed by DCT,then some region of low or middle frequency coefficients is chosen to be transformed by DHT.Last,the watermark is embedded into the region.The watermark embedded into the low or middle frequency coefficients is robust.After the two transforms,there are some host image features in the transformed region so that the tampered region and sort of watermarked image can be reflected.Simulation results show that it is effective.

Key words: digital watermark, robust, semi-fragile, DCT, DHT