Watermark Images simpler NOT Image Handler 2

Has anyone ever added a watermark to images that is not Image Handler? I don't like that IM2 renames the images and interferes with other mods, but I really like the watermark. It just seems like too much script for what I really want. I found this script that looks like it would work great, but for the life of me I can't find where one would add the code to call it.

<?php
    // this script creates a watermarked image from an image file - can be a .jpg .gif or .png file
    // where watermark.gif is a mostly transparent gif image with the watermark - goes in the same directory as this script
    // where this script is named watermark.php
    // call this script with an image tag
    // <img src="watermark.php?path=imagepath"> where path is a relative path such as subdirectory/image.jpg
    $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);
?>

you would call it with something like this

<img src="watermark.php?path=imagePath.ext&watermark=watermarkPath.gif>
or
<img src="watermark.php?path=imagePath.ext&watermark=watermarkPath.png>

I'm using slimbox, so it may not be possible or rather it may not be easy.