中文摘要：

为了提高数字水印的鲁棒性，使数字水印系统具备抵抗缩放攻击的能力，并评价其抵抗缩放攻击的程度，构造了差分特征点网格，设计了抗缩放数字水印嵌入和提取方案，并重点分析了差分特征点网格的抗缩放性能，通过分析待检图像中差分特征点的基点成功检测情况来判定数字水印抗缩放性能。在图像放大时，总能检测差分特征点中的基点；在图像缩小时，当单向的缩小比例在0．5到1的范围内，保证能够检测出差分特征点中的基点，当单向的缩小比例小于0．5，不一定能够检测出差分特征点中的基点。结果表明差分特征点网格能够较好地保证图像在受攻击后，差分特征点中仍存在基点，差分特征点网格具有较好的抗缩放性能，对数字水印抗缩放攻击起到了关键作用。

英文摘要：

In order to enhance the robustness of digital watermarking, to make the system possess the zoom resistante capability and to estimate the zoom resistance degree of the system, a difference feature point grid is constructed, and a zoom resistance embedding and extracting scheme of digital watermarking is designed. At the same time, the zoom capability of difference feature point grid is analyzed emphatically. The anti - zoom capability is judged by analyzing the successful detecting instance of basic points. If the image is magnified, the basic points can be detected all the time. If the image is dwindled, the basic points can be detected when the dwindling scale of one orientation is within the scope of 0. 5 but the basic points can not always be detected when the dwindling scale of one orientation is below 0. 5. So, a conclusion is obtained that the difference feature point grid can ensure that the basic points still exist in the difference feature points after the image suffered attacks. The difference feature point grid has a good capability in zoom resistance, and it serves a key function in zoom resistance of digital water-marking.