Paul, I've heard of a "hack" or script you can use when people are doing this.

This script pulls images (of your choosing) out of a specified directory when someone outside the site accesses the images.

For instance, if somebody wanted to link to this: , with this script in place, they would see the picture you've picked (usually a purty nasty one, like naked grandmothers or something ).

Lemme know and I'll see if I can find out some more about it.