Firstly, research on robust image watermarking. A digital watermarking scheme based on wavelet transform was proposed. It realizes the watermarking extract without the original image using 64×64×8 bit gray image as the watermark signal. In order to enhancing the security of the watermark, we employ an encryption technology based on chaos and bit plan. Simulation results show that our scheme have good invisibility and can survive low-quality JPEG compression, median filtering and so on. In addition, the analysis of the extracted watermark can help us to detect and localize tampers.