how to stop accessing of a php file from other site

Question

As i read somewhere about hot linking of images. It helps to stop stealing bandwidth of your site in case of images. Would it work for php file?

In my case, i am using a php file to generate thumbnails from an image. I dont want others to refer this php file from their site.

How can i do it?

Answer 1

One programmatic way is to check the referrer to make sure the request came from your site:

<?php
$yoursite = "yoursite.com"; //Your site url without http://
$yoursite2 = "www.yoursite.com"; //Type your domain with www. this time

$referer = $_SERVER['HTTP_REFERER'];

//Check if browser sends referrer url or not
if ($referer == "") { //If not, set referrer as your domain
$domain = $yoursite;
} else {
$domain = parse_url($referer); //If yes, parse referrer
}

if($domain['host'] == $yoursite || $domain['host'] == $yoursite2) {

//Run your image generation code

} else {

//The referrer is not your site, we redirect to your home page
header("Location: http://yoursite.com");
exit(); //Stop running the script

}

?> 

Source: http://www.knowledgesutra.com/forums/topic/40295-check-referrer-to-prevent-linking-yours-from-other-sites/

Edit
This article presents an alternate method using PHP sessions.