Duplicate Annihilator is an iPhoto duplicate finder. The application can scan for selected photos from your iPhoto library or the entire library and find duplicate images. You can configure the app to carry out different actions when it finds duplicates and you can also use a variety of algorithms to find the duplicates.
The main window consists of four tabs: Find duplicates, Analyze images, Preferences and Register. In the first tab, you can tell the app what to do when it finishes scanning and you can choose the detection mode. The options are Magic, Restrictive and Custom. In Analyze images, you can scan a selection of images. If you don't select any images here, the application will scan your entire library. Preferences is the most important tab. Here, you can choose how to compare your images to determine whether they are duplicates. The default way is MD5 checksum, and you should use this unless you want to find something particular. Here, you can also decide which duplicate you want to keep, and what actions you want to carry out when duplicates are found. Some of the available options in this regard are: move duplicates to trash, set a comment in the duplicate or original photo, clear image comments, and empty the trash when finished.
In my testing, I scanned using the Magic mode and the default settings, but I changed the actions to "move to the trash". After a quick scan, the app found 3 duplicates and deleted them from my iPhoto library.