Php + Gd watermark

Hi,

I need to generate a watermark on pictures using php and gd. I am a beginner to PHP so a little help would be appreciated.

For the first time i use this script:

<?php  

header('content-type: image/jpeg');  

$watermark = imagecreatefrompng('watermark.png');  
$watermark_width = imagesx($watermark);  
$watermark_height = imagesy($watermark);  
$image = imagecreatetruecolor($watermark_width, $watermark_height);  
$image = imagecreatefromjpeg($_GET['src']);  
$size = getimagesize($_GET['src']);  
$dest_x = $size[0] - $watermark_width - 5;  
$dest_y = $size[1] - $watermark_height - 5;  
imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 100);  
imagejpeg($image);  
imagedestroy($image);  
imagedestroy($watermark);  

?>

But the problem is that the watermark is not nice. I want to apply some shadow, transaparency etc.

You can see an example of watermark on www.private.com at pic of the day. ATTENTION ! This site contains adult material.

At the bottom-right side of picture there is a watermark with their logo. It is very clear. How can i make a clear watermark like that ?

Thank you.