Permanently deleting pics not used in albums

Hello. I have thousands of photos and videos in iPhoto. The ones I wanted to keep have all been organised into various albums (normal ones).

Without exporting every album and wiping the library and reimporting, is there a way to delete unused pics? I have tried creating a smart folder with the rule of having pics that aren't used in an album but it seems to come up with pics that ARE used in albums and pics that aren't used don't seem to be there.

Help! Thanks in advance.