That’s a question a lot of stock photographers and illustrators ask themselves. People ask me how my images get used, and I usually just say, “in advertising and marketing materials”, just to keep myself from babbling and boring them with a long story (like I’m known to do with my flapping jabber jaw). It’s even tough to explain to a normal person what a graphic designer does, and somehow people still end up thinking its CAD or something totally unrelated like that.
Anyways, back when I was a traditional graphic designer, I would horde as many stock images as I could whenever I had a stock photo subscription somewhere such as Photos.com or Shutterstock. That way, anything I had a feeling I might be able to use in the future I would be able to save on my hard drive and then use at a later date. This is something that happens a lot; so basically if you sell stock images, a lot of them are probably laying dormant somewhere on an image buyer’s hard drive. When you have a design position you begin to get a feel for which image themes and what type of imagery you go through the most, and obviously you can’t keep on using the same pics over and over again (unless you want to be a boring designer). I worked at a company that went through tons of sports, fitness, and medical related images in the custom magazines we produced for our clients. I honestly think at least half of my image sales aren’t ever even used – but who knows?
How can you find some of the images you sell in use? Go to amazon and search for your name or username/that you go by on the micros. Also try google book search in addition to plain old google. Lots of books online even have previews, and sure enough you will find your name credited in at least a couple if some of your images were used. Here are some recent finds my wife and I discovered.
Our beagle is pretty famous (he earns his Pedigree dog food, that’s for sure). Try searching for your own images if you haven’t already, and start a collection of tear sheets. You will only find a small random percentage of images actually in use, because obviously not everyone will credit your name in searchable text in each instance of use. If you don’t sell stock, but you do buy it – make a microstocker’s day by emailing them a link, or dropping them an email about how you were able to use their image! It only takes a minute, and you will no doubt put a huge smile on their face 
