06/23/2016- Update: Updated download link. I'm not really sure if this still works with newer versions of iPhoto or Photo's though.
There are many shareware tools for finding duplicate pictures in an iPhoto library but this should be a simple operation, and honestly shouldn't require a fee to utilize. As a result I created a simple Service via Automator to solve this problem.
This service is very straightforward, simply select your iPhoto library in finder and go to Services->Find Duplicates in iPhoto.
The service will do the following steps:
- Calculate the md5 of each original picture in the library. This happens to the original backup of the picture so an edited version will still get caught as a duplicate.
- Sort the list and find any pictures that have the same checksum.
- Add any duplicates found to a new Album named Duplicates. (I had intended to use a keyword but this turned out to be simpler.)
- No files are actually deleted, just flagged.
- The way iPhoto works choosing delete will just remove the photo from he album, not from iPhoto. To get around this you can select the photos from the album then switch to the all Pictures view. Your selection will remain and you can then choose to delete the selected photos.
- Download the service: Find Duplicates in iPhoto.zip
- Extract the service into the '~/Library/Services/' or '/Library/Services/' folder.