A new digital watermark technique based on digital holography and discrete cosine transform (DCT) is presented. The digital holographic watermark is embedded into an original image. Because the hologram can't be destroyed, the digital hologram watermark is constitutionally robust to cropping. It can embed more information than traditional methods. The digital hologram is obtained by the means of Fourier transform holography. In order to enhance its robustness to lossy compression, the watermark is embedded by using JPEG model and decomposing DCT coefficients. The experimental results indicate that the proposed algorithm is robust to many image operations, such as JPEG lossy compression and image cropping. And the application of security lock provides a good security. So this algorithm can be used to protect the digital multi-media's copyright efficiently.