There are web traffic tools like Awstats, others that may be provided by your IP, that many among other things can tell you what other sites are referring traffic to yours. In some cases thats good. In other cases, what that means is that people have linked to images on your site. So, when someone is viewing their site, they are also linking over to yours, taking up band width, just to view the picture, that the other sites administrator didn’t upload, thinking its easier to just paste in the link. Not a real good practice, since if the image is moved, renamed or removed from my site, then it goes missing from theirs, and now it just looks wrong.  What may be worse is that in so many cases, there is no byline mentioning the source of the image. Its good practice to mention the source of the material you are copying, instead of just leaving the viewer the impression that everything they see on your site is your work.  Anyway, its interesting to see who is using what stuff, and just how they might have found it in the first place.  Here’s a partial list of some of the sites I have found to date, though the images in question aren’t always directly related to the link, or to the front page.
This post is pictures of falls from around the world. Tons of falls pictures out there, and she included mine?
http://timepass2kstylee.blogspot.com/2008/07/falls-arround-world.html
I have yet to figure out that this site is really about and why this picture is on it.
http://www.gigposters.com/forums/anything-goes/46109-i-think-im-addicted-livejournal-image-feed-3180.html
In this case, he even says right there under the image: “Since this all published artwork, I’m linking to their art instead of republishing it. This also means that the links could die.” He provides a link to the artists site, but still links his image to the Frazz trip on my site to mine. He didnt ask me and I know this guy!
http://lambchop-rides.blogspot.com/2008/04/cartoons-and-social-responsibility.html
This bike rider blog linked to the site of the comics author, but linked the the same Frazz strip on my site.
http://irideiwrite.wordpress.com/2008/03/20/a-new-feature-at-i-ride-i-write/
A girl from an east coast college that likes long rides found the Frazz comic strip on my site about biking.
http://lizzer628.wordpress.com/page/3/
Little story about her bike ride to OHSU, and my picture of the OHSU tram.
http://flashlightfromtheheart.recesswellness.com/
This site just compiles images on a subject and it found mine.
http://peakoiljournal.com/topic/peak-oil-funny-pictures-thread-814.html
Various pictures of Mt. Himmelbjerget, Denmark. Taken during our bike ride/honeymoon trip. (Seems broken or misdirected now)
http://search.dk.lycos.de/cgi-bin/pursuit?query=himmelbjerget&cat=image&enc=utf-8&SITE=dk&color=yes&pic_size=400p
A good example:
http://pergelator.blogspot.com/2007_12_01_archive.html
I’m thinking one of these days I am going rename my images and then use those old image names for pictures of monkeys.