I have deleted a lot of photos from my computer using Graphic Converter because of its useful Find Duplicates function. Unfortunately, the thumbnails are still visible in iPhoto. Is there a way to easily delete them?
Don't change anything in the iPhoto Library Folder via the Finder or any other application. iPhoto depends on the structure as well as the contents of this folder. Moving things, renaming things or otherwise making changes will prevent iPhoto from working and could even cause you to damage or lose your photos.
Are you sure that GC deleted duplicates and not different versions of the pics?