Fooling the client into thinking php script is .jpg

I have a script that outputs an image. Using the gd library. But the only way this script gets to execute is if you call it like: www.host.com/displayimage.php That then sends the content header, and the image. Obviously I am doing some other stuff in there, which is why I am using a script to generate the image. Is it possible somehow to request the file as a .jpg? www.host.com/displayimage.jpg Fooling the client into thinking it is just a .jpg image. I tried changing the .htaccess file for the dir this script was in, so that when a 404 error is genterated, it redirects to the displayimage.php script. But its not exactly a transparent redirect. If you type an invalid url it simply redirects, displaying the name of the script, displayimage.php while loading the image. Any suggestions please?