Dup Detector freeware
http://www.prismaticsoftware.com/Utility/Utility.html
I don't speak or write english very well, so I have done a couple of screens for description how the program might be used.
Dub serie one is describing how dublicates in one or more folders, and how a datafile for further usage, is done.
Serie two is describing how to use that datafile for comparing with other picture material.
Note the screen dup2_4.jpg, it's how it look like if you not have the pictures on the place where the datafile refer to. It make it possibly to check a picture even if you not have the picture on your computer at the moment.
I have been using the default settings and it have working good.