In order to protect the copyright of the image, this paper proposes one kind of zero-watermark algorithm in DWT domain based on fractal theory. Firstly, the original image is transformed via DWT. Then, the vital features of the original image are generated by fractal matching in the domain of low frequency. After that, the dual watermark is embedded in the original image by establishing the relationship between the vital features and digital watermark image. The algorithm ideally solves the conflict between the watermark robustness and invisibility without modifying the data of original image. Meantime, simulation results show that it is also robust against common image processing and geometric distortion.