PHP GD imagecopy problem

Hi,

I want to add an icon (16x16px), black and white in .png format to an existing .png file with bunch of text. What I get is a black square on top of the image with the text. Neither of the images have any transparent background. The code I used is as follows:

<?php
$source=imagecreatefrompng("message.png");
$img_get=imagecreatefrompng("smiley1.png");

imagecopy($source,$img_get, 5, 12, 20, 20, 20, 20);

header('Content-Type: image/png');
imagepng($source);
imagedestroy($source);
imagedestroy($img_get);
?>

Any ideas why this doing this, the black squared instead of the actual icon picture? Any suggestions welcome!

Regards,

Dawid