sift的C++版，在sift上找出鲁棒性最强的几个特征点，然后以这个点为圆心，以自适应性的尺度为半径画圆，这个非常适合运用于数字水印领域，适用于抵抗数字水印的几何攻击-sift the C++ version, sift out on several features of the robustness of the strongest point, then this point as the center, the scale of self-adaptive radius circle,