BRAND your images with your URL kinda like the attached (or even MORE blatantly), *AND* use Photoshop (or Paintshop Pro) to embed a watermark (the little secret digital code they can't see but you can "trace").

Then ask the imag-stealing offender to remove the images OR remit $1500 a year PER IMAGE fee to your over-priced graphics guy for a 1 year license to use the following pictures, because his lawyer is a pitbull and you wouldn't want him thinking YOU were violating his copyright. I usually FAX or attach an "order form" and those images start disappearing lickety split!

If THAT doesn't work THEN contact eBay or the ISP/Host of the person violating your copyright and most times they'll remove the images or nuke the account.

Then there's always CEASE & DESIST, but they didn't cover that in art school.