Once I had had a similar incident. The guy took not only my pictures, but he pointed his listings directly to the pictures that were on my host! The guy was stealing my pictures, item description AND my bandwidth!!!
I got really mad and started writing a nasty email.
Then, I had a better idea... I replaced all the pictures on my host with some 'different' material ]:) . Then I monitored how long it would take someone to notice. A few days later, the listing was pulled, and the user NRU'd!!!
I know that was bad. A little time consuming, but very satisfying in the end.