[GD] watermark che non funziona

[cubalibre810]

<?php
$source = "ciao.jpg";
$watermark_file = "wm.png";

$image = imagecreatefromjpeg($source);
$source_w = imagesx($image);
$source_h = imagesy($image);

$watermark = imagecreatefrompng($watermark_file);
$watermark_w = imagesx($watermark);
$watermark_h = imagesy($watermark);

$dest_x = $source_w - $watermark_w - 5;
$dest_y = $source_h - $watermark_h - 5;

imagecopy($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_w, $watermark_h);

header('Content-type: image/jpeg');
imagejpeg($image);
?>