image watermark with php

<?php  
 
$main_img 		= "image.jpg"; // main big photo / picture
$watermark_img	= "watermark.gif"; // use GIF or PNG, JPEG has no tranparency support
$padding 		= 3; // distance to border in pixels for watermark image
$opacity		= 100;	// image opacity for transparent watermark
 
$watermark 	= imagecreatefromgif($watermark_img); // create watermark
$image 		= imagecreatefromjpeg($main_img); // create main graphic
 
if(!$image || !$watermark) die("Error: main image or watermark could not be loaded!");
 
 
$watermark_size 	= getimagesize($watermark_img);
$watermark_width 	= $watermark_size[0];  
$watermark_height 	= $watermark_size[1];  
 
$image_size 	= getimagesize($main_img);  
$dest_x 		= $image_size[0] - $watermark_width - $padding;  
$dest_y 		= $image_size[1] - $watermark_height - $padding;
 
 
// copy watermark on main image
imagecopymerge($image, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, $opacity);
 
 
// print image to screen
header("content-type: image/jpeg");   
imagejpeg($image);  
imagedestroy($image);  
imagedestroy($watermark);