php dynamic image watermark

<?php
    $imagesource =  $_GET['path'];
    $watermarkPath = $_GET['watermark'];
    $filetype = substr($imagesource,strlen($imagesource)-4,4);
    $filetype = strtolower($filetype);
    $watermarkType = substr($watermarkPath,strlen($watermarkPath)-4,4);
    $watermarkType = strtolower($watermarkType);
 
    if($filetype == ".gif")  
        $image = @imagecreatefromgif($imagesource);
    else  
        if($filetype == ".jpg" || $filetype == "jpeg")  
            $image = @imagecreatefromjpeg($imagesource);
        else
            if($filetype == ".png")  
                $image = @imagecreatefrompng($imagesource);
            else
                die();  
 
    if(!$image) 
        die();
 
    if($watermarkType == ".gif")
        $watermark = @imagecreatefromgif($watermarkPath);
    else
        if($watermarkType == ".png")
            $watermark = @imagecreatefrompng($watermarkPath);
        else
            die();
 
    if(!$watermark)
        die();
 
    $imagewidth = imagesx($image);
    $imageheight = imagesy($image);  
    $watermarkwidth =  imagesx($watermark);
    $watermarkheight =  imagesy($watermark);
    $startwidth = (($imagewidth - $watermarkwidth)/2);
    $startheight = (($imageheight - $watermarkheight)/2);
    imagecopy($image, $watermark,  $startwidth, $startheight, 0, 0, $watermarkwidth, $watermarkheight);
    imagejpeg($image);
    imagedestroy($image);
    imagedestroy($watermark);
?>