防伪技术一直是人们关注的一个热点，针对印刷品盗版特定场合防伪存在成本较高的问题，在分析印刷扫描给电子图象带误差的基础上提出了一种用于印刷品防伪的数字水印技术，该方法中水印的添加采用了线性运算，而水印的提取则采用了阈值判断法，在提高算法的鲁棒性方面，水印的构造采用了简单但非常有效的重复构造法，另外，为了保证实验结果的稳定性，算法还采用了CIElab色彩空间，实验结果表明，在对参数优化后，该算法能较好的满足防伪的一般要求，同时与其他防伪技术相比，不仅大大减少了防伪成本，而且该算法还可用于普通证件的防伪。

Forgery prevention and detection are of great social importance.This paper attempts to apply digital watermarking into forgery prevention. The digital watermarks are embedded into the most important DCT coefficients except the DC coefficient of the original image through linearly additive operation.The corresponding watermarks are extracted throught threshold judgement and the threshold is determined through the difference of two cycle print&scan and one cycle print&scan of the images.To improve the robustness of the algorithm,the simple and effective repetition is applied to watermark configuration.And the CIELab color space is chosen to guarantee the repetition of the results and minimize the error brought by the transference of images between differnt equipments.Experimental results show that the proposed algorithm can satisfy the requirements of forgery prevention for ordinary images,that is to say the digital watermark is robust to one cycle print&scan and fragile to two cycle print&scan. Compared with other forgery prevention and detection techniques,the algorithm described in this paper reduced the computation cost considerably as no other special material or equipment is required and ordinary user can verify the authentication of printing materials. This algorithm can also be used in printing materials copyright protection,such as the owner verification in certificates,passports,ect.