Ask the hive mind - A program to match pictures

[lightcastle]

In an attempt to put some order in some of my harddrives, I figure I need to strip some of the various duplicates that I have. For music I've used media monkey in the past, which was ok. I've also used Fslint for just a generic "do these files match" approach. I know there are now programs which supposedly match pictures based on face recognition or other such criteria, which could be very useful when I have multiple copies of something similar at different resolutions. Does anyone have any experience with any of these? Any recommendations for a balance between usefulness and cost for those of us who are desperately poor?