Have you ever seen one of your photos being used without your permission? I have, and although at first I was flattered that they liked my work enough to steal it, I felt violated. They really could have asked.
So how can you tell if there are images of yours floating around the web, that you don’t know about? Easy. Open Google Images, and drag one of your photos (low res works fastest) into the search bar. Google finds sites that have the same image, as well as a list of visually similar images.
This is how it looks – although this image was used with my permission!