Actually, I have recently been informed by a fellow geek of some
extremely shady activities by one of those stock photo companies. The speculative cheeky b*****ds sent her a demand for
over £900 for a piddly little image for which they claimed copyright that was on her web site (and she didn't even put it on there - her web designer did).
Now it would also appear that there is a company out there called PicScout who runs "bots" (automated software programs that crawl the Web) - but theirs are of a rather more sinister nature than those of Google and the rest of the search engines. The purposes of their bots is to trawl the Web looking for "unlicensed images", and they have a fancy algorithm that's using some sort of steganographic watermarking to identify if the image is one of their copyrighted ones.
The following link gives some more in-depth technical information about their tactics:
PicScout, Getty Images and Goodbye iStockPhoto..!
Now I'm getting a bit paranoid, because even though I've done a couple of sites for people that use (legitimately purchased) images from iStockPhoto, I don't trust the sort of tactics that these guys use, and frankly haven't got the time to deal with "spammigation" (speculative automated bulk legal action) - we had enough of that last year with the likes of Lowell Group (a debt collection agency) attempting to chase Sonia for a non-existent debt from a mobile phone account that would have been older than 6 years anyway, and so legally unenforceable. But thanks to that article in the link above, I've updated my Linux firewall to block all known IP addresses from PicScout, so if they try to waste my server bandwidth speculatively looking for supposedly copyright infringed images on there, then they can go jump, as they'll just be wasting
their time, as my firewall will be dropping all their packets, so they'll have to wait a good while for the TCP/IP connection to time out, ha ha!!!