PHP 两张图片合成一张图片（加水印）

$dst_im = 'http://www.wangshangyou.com/content/uploadfile/201312/b3241386050881.png';
$src_im = 'http://www.wangshangyou.com/content/uploadfile/201312/72691386051117.png';

$dst = imagecreatefromstring(file_get_contents($dst_im));
$src = imagecreatefromstring(file_get_contents($src_im));
list($src_w, $src_h) = getimagesize($src_im);
//imagecopymerge($dst, $src, 10, 10, 0, 0, $src_w, $src_h, 50); 
imagecopy($dst, $src, 50, 680, 0, 0, $src_w, $src_h);


list($dst_w, $dst_h, $dst_type) = getimagesize($dst_im);
switch ($dst_type) {
    case 1://GIF
        header('Content-Type: image/gif');
        header('Content-Disposition: inline; filename="image.gif"');
        imagegif($dst);
        break;
    case 2://JPG
        header('Content-Type: image/jpeg');
        header('Content-Disposition: inline; filename="image.jpg"');
        imagejpeg($dst);
        break;
    case 3://PNG
        header('Content-Type: image/png');
        header('Content-Disposition: inline; filename="image.png"');
        imagepng($dst);
        break;
    default:
        break;
}
imagedestroy($dst);
imagedestroy($src);
exit;