Have a look on this wikipedia link displaying available open source software for this task.
http://en.wikipedia.org/wiki/List_of_duplicate_file_finders
I will add that the GUI version of fslint is very insteresting, allowing to use mask to select which files to delete. Very usefull to clean duplicated photos.
On Linux you can use:
- FSLint: http://www.pixelbeat.org/fslint/
- FDupes: https://en.wikipedia.org/wiki/Fdupes
- DupeGuru: https://www.hardcoded.net/dupeguru/
The 2 last work on many systems (windows, mac and linux) I 've not checked for FSLint