Abstract: The image watermark is encrypted by the logistic-map sequences in chaotic dynamical systems.And error correcting technology is adopted.The idea of embedded synchronic signal introduced in the algorithm is proposed，which uses the synchronic signal for locating the watermark location.The watermark and synchronic signal are embedded into the DCT low frequency components by quantization.The embedding strength is adaptively controlled by the masking threshold.Experiment results show that the proposed watermarking scheme is inaudible and robust against various signal processing such as lowpass filtering，noise adding，re-sampling and cutting.