If you post it on the internet, or have it in public view, anyone can use it or take a picture of it because its in the public domain. This includes pictures of yourself in public view (even in your own yard) unless used for commercial purposes. If you have it copyrighted,or trademarked, you do have legal recourse, but as others have pointed out, its rarely worth the bother. They are very difficult cases to prove and unless the offender has made a LOT of money using your image, no lawyer will take the case.
