The title is sort of a joke. When you have about the only good pictures of an item on the internet, you are bound to be the target of people who want to use your image on their site. But most of them go about it the wrong way. They use a direct reference to your image instead of downloading it and uploading it back to their server.
You could cut the problem out by watermarking all of your images when you add them to the site. But that would take all the fun out of what I am about to tell you.
You could get pissed. Call the site's owner and bitch at him. But there are other options. One thing you could do is stop people from doing it. Another thing you could do is let them do it and sit back and wait.
And when they aren't looking, either watermark your images that are getting hotlinked will your url or switch out the image entirely. With luck someone that hotlinks your image will be a direct competitor or will be having an auction on Ebay, but sometimes it's a blog.
To find which images on your site are being hotlinked, you have to have some sort of web site statistics software installed on the site. Check your links from an external page section. That is the hits that aren't coming from search engines, but from other sites. Scroll down this list. When you find one that shows hits but no pages loaded, go to that site and see if they are using your picture.
If they are, you can use a picture editing program to add your url to the picture. And if you no longer use the picture on your site, you can go all out with address and phone number.
Just a note, if this post is a few days old, the links above may not show the images I am referring to.