A year ago, in an effort to really organize everything, I purchased Aperture 3 (after using the trial for a month). I tried importing all my old photos from all my old machines, hard drives and cameras onto my current laptop. I managed to very quickly fill up my 500GB hard drive and my goal of photo organization was no closer to reality than when I had originally set out on that mission.
On several inspired weekends, I decided to try to sort through the collection of Projects, Albums, and Folders in an attempt to identify which photos were duplicates and which were originals. My latest attempt yielded more frustration so I turned to Google, where I found a few apps devoted to sorting through duplicate photos in Aperture. Initially, I found Duplicate Annihilator, which has a 500 photo trial version (full price $7.95). It found 4 duplicates within the 500. I wasn't ready to jump in for the full eight bucks, so I decided to check the Mac App Store to see if there were any alternatives.
I stumbled across DupeZap, which normally retails for 15 dollars, but was on sale for .99. Sold! The app not only helps with photos, but with all duplicate files. This is great for me because I'll occasionally download multiple copies of the same Photoshop file or presentation during the course of a project.
DupeZap is better than some other competitors because it searches through your Aperture or iPhoto library folders. It's also not destructive, which is great for people who like to double check things. On a first pass, it found nearly 1,500 duplicates (or triplicates) in my photo library. I was then able to review each of its discoveries one by one (not required, but I like to double check). I then tagged each one for deletion, which essentially adds some metadata to each photo (in this case the keywod Duplicate_Master_to_trash). In Aperture, I created a new album that searched for that keyword. In that new album were all the photos that DupeZap found as duplicates and I had marked for destruction. I then moved them over to the Aperture trash and voila, cleared up nearly 2 GB of hard drive space. I did this process twice, once for master images and a second time for versioned images.
On the whole, DupeZap is easy to use, has a great interface, and lets me do most of the identification work without having to go into other programs. I would highly recommend this at $.99, and while $15 might seem steep, it's a lot cheaper than a new hard drive. You can download it on the Mac App Store via this link.