Image file comparison - removing duplicates

I have (and a few friends) a LARGE number of image files, pictures, that is, that need ordering and cleaning up. Now, I could go through them manually, to remove identical images, but this might take several days, and would be VERY laborious. Is there a program that identifies identical images by their content, and not by their filename? Ideally this program would allow for the deletion of identical files, preferably automatically. In other words, it would have to compare the pixels of each image, or some hard-coded identity tag, to determine which ones are identical and which ones are unique.

This would hopefully leave me only with unique files, each with their respective file-stamps - which are what I require for their ordering (using my little program, see the website ).
Did anyone come across such a program?

Have you tried Duplicate File Finder:

http://dff.nazrashid.com/

Thanks. Freeware as well

I was advised on another good program, AcuteFinder, http://www.hugmot.is/acutefinder/
It's not free however....