Digital watermarks have been proposed in recent literature as a means for copyright protection of multimedia data. The robustness and the imperceptibility are the basic requirements of the digital watermark. In this paper

we propose a digital watermarking algorithm based on Shamir secret sharing scheme. We divide the field of the image into parts

and then we also make the information of digital watermarking into shares by the algorithm. We embed each share of the digital watermarking in the corresponding part of the image by contrasting DCT coefficients， and only need arbitrary shares in the recovery progress. In order to enhance the precision of the extracted watermark

we improve the extracting algorithm based on fuzzy set. Experimental results show that this algorithm has a good hiding effect and is robust for single attack and even collage attacks.