网络请求图片，根据范围取图

CGImageRef temImg = image.CGImage;

float width = CGImageGetWidth(temImg);

float height = CGImageGetHeight(temImg);

temImg = CGImageCreateWithImageInRect(temImg, CGRectMake(width * 0.5 - height * 0.5, 0, height, height));

//得到新的图片

UIImage *new = [UIImage imageWithCGImage:temImg];

shopImage.image = new;