Good FOSS Duplicate File Finder For OSX
duff ... I found it to be faster than fdupes, and it's easier to use in scripts. You can get it via Homebrew.
I like FSlint on Linux, with any luck it'll build on OSX. Unfortunately I don't know of any good FOSS duplicate image finder, I have to use Windows ones like XNView.
You can install fdupes from Homebrew. It's a generic duplicate file finder for the command line.