What are some alternatives?
When comparing Duplicate File Finder Plus and Duplicate Cleaner, you can also consider the following products
AntiDupl - AntiDupl.NET can find and display duplicate images in the main graphic formats: JPEG, GIF, TIFF...
dupeGuru - dupeGuru is a tool for finding duplicate files on your computer.
FSlint - FSlint is a utility to find and clean various forms of lint on a filesystem. I.E.
VisiPics - VisiPics does more than just look for identical files, it goes beyond checksums to look for similar...
Easy Duplicate Finder - Free download! Find and delete duplicate files with Easy Duplicate Finder™. Get rid of annoying duplicates on your Windows and Mac.
Pixiple - Find images similar in pixel and/or metadata content