BRATTOO PROPAGANDA SOFTWARE There are several freeware and commercial utilities such as the suggested Image Comparitor that locates duplicate files in the filesystem. However, when locating duplicates in iPhoto it is not sufficient to remove the files since the iPhoto library data base will then be corrupted since it points to image files that does no longer exists in the iPhoto library package.
Therefor, a word of advice: Messing with the files in the iPhoto library package or folder may cause a corrupt iPhoto library database and or loss of data. Therefor, be careful when attempting to use a generic duplicate detection tool when hunting for duplicates in iPhoto.
Duplicate Annihilator is not a generic duplicate detection tool but a tool designed especially for iPhoto and only Apples own API's and recommended methods when manipulating the iPhoto library and the images.
(Version 2.17.3)