The internet is so big, there really is nothing you can do. You can do a reverse search on Google to see if anyone is using your image on the internet. I found some one using one of mine as a avatar on a sports forum. Every image has its own unique "DNA". Google searches the web for this DNA. I am not sure if the DNA can be changed, but I am sure it can be.

I did catch an "artist" on a photography page on Facebook. He was stealing images and reprocessing them. He sells images on the street down in the French Quarter in New Orleans. I am not sure if he is selling only his images or all images he has. All I could do was get him kicked out of the club. I reported it to FB, but they did nothing.