In reviewing the log files on my site, I noticed a new crawler I had not seen before, one which crawls for images only. Going to their site, to my surprise I found one of my older images -- on someone else's site and with their logo on it! I checked out the site and, sure enough, there was my image. In this particular case, it was an older image from some years back, made in my pre-digital days. It was a composite, made from several photos put together, so there was no mistaking it.
The site which is using the image, maps-of-mexico.com, claims something like 2,500 images on their site, which makes you wonder just how many of them are pirated from other sites.
Since most of my sites are heavily dependent on photos I have made (one is approaching 500 images at the moment), I feel I should do something or they'll just keep getting more from other folks as well. I've been reluctant (and too lazy) to put logos or watermarks on my images, because they detract.
What would be my best approach to this offending Web site? Anybody else with similar experiences?

Memo

Well.. Email the webmaster. They might not even know if they got it from another website i.e. the website that did the crawling.