Software that will analyze photos and delete duplicates.

Hi I have so many Duplicated photos its unreal. Well I had all my photos nice and sorted once and about 100 things happened and I have copies out the roof. Some are big and some are small as well. Because somehow the data files from my iPhoto library got mixed in and there are smaller versions of the photos.

I have been working for days reorganizing my Photos into new Folders and once I have my 40,000 photos back into their correct folders I was hoping that It would be easier to get the duplicates deleted. But I still have to sort the Photos First.

Is their some kind of software that can help me. Please

Note: I have been working on and off on this project for a few months now. And by the way when i say 40,000 i mean that how many I have left to sort. I know that half of that are duplicates. And 15 % are photos i know i don't want.