iPhoto Duplicate Cleaner is a nice utility that can help you get rid of duplicates. iPhoto is a great application to store your photos in different libraries and manage them, but the application doesn't really help you with one of the problems common to large collections of photos: duplicates. That is why iPhoto Duplicate Cleaner was designed. This application can scan your libraries and show you all the duplicates in a clear way. Then, you can take action and remove the duplicates.
After the application has scanned your iPhoto libraries, it will display a message stating how many duplicates it has found. All the duplicates, along with the original photos, will be displayed for you to see in a single window. You can then select the files that you want to delete by checking a box next to them. The duplicates are already selected automatically when the scan is completed. By default, the program will only display duplicates, but if you venture into the application's preferences window, you will be able to tell it to treat edited copies as duplicates. After deleting your photos, you still need to go to iPhoto to delete the trash. Until you do that, the photos will be still on your hard drive and they will even be found again in future duplicate scans.
In my testing, the application found a single duplicate in my library. I don't have a lot of photos, so the scan was quick. It took a little less than 3 seconds for a library with a few thousand pictures, which isn't bad.