If someone has a graphic call from a URL that's not one of your listed URLs, one of two things happen.
If the call is embedded in a page (i.e., with a head and body and all) they get a broken graphic - not found. If it's just a call for the graphic like http://www.domain/graphic/mike.jpg - which is usually the case - then they get a substituted file of your choice. Usually you give them a page with some banners for them to click on.
Not only does this reduce your bandwidth by stopping hotlinkers,
but you actually generate revenue from it instead!

Here's all you have to do to make use of this feature: put a file named ".htaccess" in any directory on your site. Any attempt to access any file in that directory will invoke the rules contained in the file. If the referring URL is not listed in the file, the "RewriteRule" page will be sent instead.

A sample .htaccess file:

AuthUserFile /dev/null
AuthGroupFile /dev/null
 
RewriteEngine On
RewriteCond%{HTTP_REFERER} !=http://fred.com/main.htm
RewriteCond %{HTTP_REFERER} !=http://wilma.com/main.htm
 
RewriteRule /* http://fred.com/hotlink.htm [R,L]

This limits access to the files within to the two "RewriteCond" URLs specified.
If any other URLs try to access any file in the directory, http://fred.com/hotlink.htm is delivered instead.

Updated: 03/17/03