UIGraphicsBeginImageContext(image1.size);

        [image1 drawInRect:CGRectMake(0, 0, image1.size.width, image1.size.height)];

        [image2 drawInRect:CGRectMake(image1.size.width - (image2.size.width * 0.5),

                                      image1.size.height - (image2.size.height * 0.5),

                                      image2.size.width * 0.5, image2.size.height * 0.5)];

        UIImage * image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();

//image就是加水印后的圖片   水印位置在右下角