I would contact the seller first, and ask for... (what ever you feel the usage is worth).
If you get no satisfaction that way, contact EBay and tell them about the unauthorised use of the image, the auction will be pulled within minutes.
Just because the bidding is at $10 now, doesn't mean it won't go much higer later. Besides, it's the principle too, right?
One day, I might be good at this...