In order to enhance the robustness of digital watermarking, to make the system possess the zoom resistance 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 to 1, 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 watermarking.