Show HW: PlaceSheen
placesheen.comYou'll probably want to disallow stuff like this: http://placesheen.com/phpthumb/phpthumb.php?src=http://cvcl....
Look in phpthumb.config.php for $PHPTHUMB_CONFIG['nohotlink_enabled'] and make sure its set to true.
If you need to enable it for some domains you can do that too: http://phpthumb.sourceforge.net/demo/docs/phpthumb.faq.txt
Edit: you should turn off debug too: http://placesheen.com/phpthumb/phpthumb.php?src=xxx.jpg&...
While these are fun, if you want something more serious: http://placehold.it/
Are you ready to roll to kittens at a moment's notice, in case Sheen kills someone (possibly himself)?