Detect duplicate files before importing to iPhoto?

Not sure if this should go here or the iPhoto categrory. Over the years I've had lots of different computers, sometimes a PC sometimes a Mac etc. I've reinstalled and so on so my picture library is messy. I've done work on my new Mac Mini to clean everything up in iPhoto, but I have some DVDs and back up drives that have pictures or backups on them from older computers.

I've noticed that a lot of the pictures on there are already in iPhoto with some that aren't. Same goes for videos, most are in there already like 90% or so are in there.

Is there an app or something I can use to run against a folder recursively (being the backup) to have it show duplicates in iPhoto? Ideally it would be great if it compared the two, so obviously matches by name, but then shows the results with a thumbnail so I can actually see if it is a duplicate and from the app just delete the backup copy etc. There's so many folders and sub folders that it's really tedious checking to see if they are already in there or not so thought I'd check. Thanks!

Decloner can help

My app Decloner (decloner.com) can do that. You can scan for duplicates across multiple iPhoto and Aperture libraries and ordinary folders at the same time. There is a fully functional 30-day trial available, you could give it a go and see if it works for you.