Checking Original URL

I have a file "image_server.php" that receives requests through <img> tags & GET variables, and returns the requested image with PHP GD support. That runs all fine and dandy, but I want to check the absolute URL that is calling it to make sure it is an approved URL. (For example, I need the URL of the HTML file that contains the <img> tag that is requesting the image from the php script) I have tried $_SERVER['REQUEST_URI'] but that just returns the path to the php script file. Is there a different variable that I can use? I haven't exhausted all of my searching, but figured a question here would save me some time! I'll keep searching in the meantime! Thanks in advance . . . -- The Disguised Jedi disguised.jedi@gmail.com PHP rocks! "Knowledge is Power. Power Corrupts. Go to school, become evil" Disclaimer: Any disclaimer attached to this message may be ignored. This message is Certified Virus Free