I am an artist and designer and have numerous websites out there featuring alot of my art and designs. During the past few years I have stumbled across many websites, personal ones and also large mainstream ones featuring some of my images. For example the most recent one was last week. I came across this tattoo website that had a link to angel tattoos. To my amazement the only image they had was one of mine. At first I was mad but when I clicked on the enlarged image I could see my website URL under the design aswell as the copyright symbol. I don't know if their taking the piss or respected the fact that they got it from one of my sites.... Another time a few weeks ago somebody was selling 1000 designs on ebay. The thumbnail image they were showing for their advert featured some of my designs. That pissed me off, so I did contact ebay and the seller, but have not yet had a response and he is still selling designs using my designs for his advert.... So my question is, if it was you how would you go about tackling this problem?
I would do as contentboss said. Many people use watermarks in their images to protect their work. The best way I have seen is to hide it within the image so that it blends in and only you can identify its location in the image. You can find some good tools and ideas on this link. Some of them are about invisible watermarks and digital fingerprinting. http://www.riecks.com/security/
Helmet right between the numbers, then drive with the legs. At least that is how I learned to tackle.