“Track and delete iPhoto images that aren’t in any album ” by Mac OS X Hints is a tip on managing your iPhoto library, specifically getting rid of orphan photos.
iPhoto ‘09 has a “Smart Album” feature that enables you to track down pictures that are not in any albums. Follow the directions in the Mac OS X Hints article to create a Smart Album that updates itself with orphan photos — those that are not in any albums — and then use it to move those picture to the trash.
Warning! These directions result in the orphan photos being moved to your trash and possibly being deleted permanently. Before you follow these directions, be absolutely sure that you wish to delete the photographs found by this Smart Album.
