说明：  一种针对分块数字图像水印中图像块的选取选取方法，主要有基于边缘检测和方差这两种，程序对这两种方法进行了仿真与对比
(a method of selecting the image blocks in block based digital image watermarking is mainly based on the two kinds of edge detection and variance, and the two methods are simulated and compared.)