在主图上移动和改变选框的大小，通过Javascr ipt实现截取该选框内部的图像选区，并且把选框的长宽，选框距离各个边框的位置，动态的显示出来，实现用户根据需要截取一张大图的局部。-Move and change the marquee the size of the main map via Javascr ipt to achieve the interception of the marquee of images within the constituency, and the leng