在做图片裁剪的时候 裁剪完的图片在回调的时候多出引用需要copy UIImage没有实现copy的方法，要想copy有几种方法可以实现
UIImage *smallImage = [UIImage imageWithCGImage:[originalImage CGImage]];
2.CGImageRef newCgIm = CGImageCreateCopy(picImage.CGImage);
UIImage *newImage = [UIImage imageWithCGImage:newCgIm scale:self.picImage.scale orientation:picImage.imageOrientation];
CGImageRelease(newCgIm);
3.UIImage *newImage = [UIImage imageWithData:UIImagePNGRepresentation(oldImage)];
