Do you have duplicate or triplicate photos in your iPhoto Library? I recommend using Duplicate Annihilator to remove them. The developer’s web site has a short movie that shows you how to use the program. It is reasonably priced at $8 for a single license or $13 if you want a Family Pack which lets you install it on as many as 5 Macs. While I trust Duplicate Annihilator, you should always make sure that you have a complete backup of your iPhoto Library before you use Duplicate Annihilator. Its default settings will not delete any photos from your iPhoto Library. Instead, it assigns the word duplicate as a comment for each duplicate photo that it identifies. By default, it uses an MD5 checksum to compare photos. This is a very effective and accurate way to compare digital fingerprints of two files to see if they are the same. Duplicate Annihilator can take several hours to scan a library with tens of thousands of photos, so be prepared for this. It displays some status indicators such as a running total of duplicates found, how many photos it has scanned, how many photos remain to be scanned and estimates how much longer the scan will take. Once the scan is complete, you can enter the word duplicate in iPhoto’s search field to locate all of the duplicates. Then you can go to the Edit menu and choose Select All to select the duplicate photos, then press the Delete key on your keyboard to put these photos into iPhotos’ Trash. Then you would need to empty iPhoto’s trash to completely delete the photos.
Important Note: Before I delete the duplicates, I like to do some random double-checking. After I’ve used iPhoto’s search feature to locate the duplicates, I write down the date of a handful of the photos. Then I clear out the search field so I can see all of my photos. After that I locate these selected photos by date to verify the photos are, indeed, duplicated. Finally, I repeat the search to locate all duplicates and delete them.
Check out Duplicate Annihilator. It can save you a lot of time when you need to eliminate duplicates in iPhoto on your Mac.