针对2维工程图版权保护问题，提出了一种基于差值扩大法的2维工程图的水印嵌入算法。该算法对差值扩大法进行改进解决了工程图线段顶点坐标值相关性差的问题，通过修改线段端点的坐标值来嵌入水印信息。由于修改量非常小，不会产生视觉冗余。提取时可以精确地恢复原始工程图，满足了工程图加工精度高的要求，并且实现了盲提取。实验结果表明该算法达到了较好的效果，并且易于实现，适用于工程图的版权保护领域。

In order to take effective copyright protection for 2D engineering drawings，the paper presents a reversible watermark embedding algorithm based on difference expansion for 2D engineering drawings. The algorithm works on the feature of poor relevant of vertex coordinates of lines in engineering drawing, embedding watermark information by modifying the vertex coordinates of lines. Because of minute revision, there isnt any visual redundancy. During information extracting, the algorithm can restore the original engineering drawing accurately, and meets the requirements of high-precision machining, and also realizes the blind extraction. The experimental results show that the algorithm achieves good results, and easy to implement, it can be applied to the copyright protection of engineering drawings, content certification,information secret transmission and other fields.