I have been working on consolidating my photos from several different computers into one definitive iPhoto library with all of my digital photos. After reimaging computers at school and restoring files to the way they were before the reimaging (as best we could), we had several people with multiple copies of photos in their iPhoto libraries. Duplifinder solved this problem for me.
When I began searching for a solution I came across a thread on Mac Rumors that led me to some possibilities. I spent a couple of hours researching the different software solutions, reading the literature, and testing them out. I really liked Tidy Up!, which I found on the OS X Mac Tips & Tricks blog. Tidy Up! will also find duplicates in your iTunes library and several other places on your Mac. The reason I decided not to buy it is the $33 price tag. I also checked out Duplicate Annihilator, but didn’t get the visual representation of the photos I wanted. The software I finally decided on is Duplifinder. Only $7 and it went through my entire 13,000+ iPhoto library, found all the duplicates, and gave me the option of deleting all the duplicates in one click, or one at a time. Duplifinder is a great tool at a very reasonable price. I recommended it to my entire staff.