netmeg - 8:18 pm on Mar 9, 2011 (gmt 0)
I have issues with scrapers too, although my scrapers are usually "legitimate" sites such as newspaper and television websites. (And unlike most people, my policy is that you can take anything you want off the site as long as you attribute it to me)
You simply can't rely on any programming or algorithm to deal with the problem, you have to take it upon yourself.
So my first step in this situation would be to try to figure out how they're scraping the site, and whether there's anything I can do to make it more difficult. If they're just coming along and screenshotting pages, there's not a lot you can do about that. But on the plus side, that method doesn't scale very well.
Me, I'm a log file/analytics junkie. I'm always looking for anomalies and unusual behaviors.