like how clubphoto now does....you post on say a forum and get an error thing...how do i set this up? and how do i make it so that way they get a message image? thanks!

Search google for mod_rewrite

You can add it to your htaccess file.

If your host has CPanel, you should be able to use the Hotlink Protector feature to prevent hotlinking. :D

http://www.javascriptkit.com/howto/htaccess10.shtml
^.htaccess
http://www.thesitewizard.com/archive/protectimages.shtml
^PHP (This one just doesn't show the actual URL of an image)