Well, that's a pretty good question. I suppose if you know what you're looking for you could peruse your server logs. I accidently discovered a 'leecher' one time, by placing the full link of an image in Google and searching. My goal was to see if Google would point back to my site and they ended up showing me where, on another site, my link was!
I uploaded a small gif to my blog one time and found out that some guy on a Spanish forum was using the gif on my server as his avatar! The cheek! Only noticed it when I checked the server logs and saw a lot of traffic coming from some Spanish site i didn't recognise, it was the site coming to grab the gif off my server to display his avatar! Needless to say; that file got quickly renamed!
I caught two people doing this. The first was an automotive parts company that hotlinked to an image of my custom door handle on my pickup. I changed that image to some xxx porn, it showed up on his company website for almost a week before it was removed. Second was a few weeks back, someone used one of my pics as his Myspace page background in a tiled format, I changed it to something else creative and it was removed in a few days
I use to have this problem bad on my clipart site. I eventually installed a script that hides the image's true location and then loads the image in the src tag. This prevents others from leeching them.
I use awstats to check my traffic and if you look at "Connect to site from" and then check "Links from an external page (other web sites except search engines) - Full list". You can see which pages use your pictures when you only got hits instead of pages + hits .
you can always check your stats - something like AWSTats or Webalizer even probably shows the files with the maximum usage in kb as well as wher frm .
That's the same method I use. That's how I tracked down countless MySpace profiles that hotlinked to rather large images for use as their backgrounds. Bandwidth thieves. In any case, I've now just preventing hotlinking in total. Makes life much easier.
It happened to me that a "designer" used a tri fold brochure I had designed in his Myspace showing it as portfolio of his work. The most incredible thing is he didnt even bothered in downloading the pic and hotlinked my server......just pathetic
It happended to the website of the company I work at. Some competitor was hotlinking one of our pictures. So I've replaced the hotlinked picture with a very cool custom made banner. Now we have a free banner on his website.
I got another one today Minor Work Warning - image is small http://www.vmlp.com/wbag.htm They were linking directly to the dodge logo on my business website. Maybe this will stay there through the Thanksgiving break At least they could be smart enough to save the image to their own webserver
On the script I'm about to launch if anyone hotlinks the content a pop-up message appears on their site warning visitors the content is stolen. Doesn't prevent them from using it, but will give them a bad image.
You'll probably increase their customers, visitors will they they get a free lapdance or something if they purchase a car haha.
I had a issue once. A site hotlinked a picture from my clients site. So I wrote to the webmaster about removing it. He just apologised and said that he thought hotlinking will not have any copyright issues since he did not copy the image. He removed the image immediately.
Here's what hotlinking looks like in AwStats: The first column is for pageviews. The third is for hits. Zero page views, but hits = hotlinking.