Abstract:An improved watermarking algorithm is proposed to deal with public watermarking verification and large information reserves. This algorithm is based on two dimensional discrete Fourier transform (2DFT). The phase of the reference watermark is shifted randomly in the 2DFT domain to obtain many embedding watermarks. They are correlated with one another and have the same correlation with the reference one. To decide the presence of the watermark, the detector compares the correlation coefficient with the decision threshold. The simulation results show that with the proper threshold, the reference watermark can be used to detect the embedding watermark, but other embedding watermarks cannot. The publication of reference watermark does not compromise the embedding one. This algorithm realizes the public verification of watermark, and needs only one reference watermark for detecting embedding watermarks, which decreases the watermark storage.