Watermarking uploaded images

It would be great the option to watermark the images uploaded by imagefield.

I've done a fast attemp and now it's working fine for me. It is just insert a few lines after the resizing action:

[line 325, just before the "return $file;", add this]

if ( $width > 400 ) {
$watermark = imagecreatefrompng('./watermark.png');
} else {
$watermark = imagecreatefrompng('./watermarklow.png');
}

$watermark_width = imagesx($watermark);
$watermark_height = imagesy($watermark);
$imagen = imagecreatefromjpeg($file['filepath']);

$size = getimagesize($file['filepath']);
$dest_x = $size[0] - $watermark_width - 5;
$dest_y = $size[1] - $watermark_height - 5;

imagecopymerge($imagen, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 50);
imagejpeg($imagen,$file['filepath']);
imagedestroy($imagen);
[...]

As you can see I've inserted a previos "if" because I wanted to have two different watermarks, depending on the size of the image...

As I said before, this is a fast solution, but it would be nice to have it better developed in the imagefield.module.