On the iPhoto File Structure
I could condense all my iPhoto wisdom in one sentence: for your own benefit, please never, ever open the iPhoto folder library folder and move files around. That’s it. This is because iPhoto has to maintain a very strict inventory of its data. The data structure is explained here:
http://www.iphotolibrarymanager.com/Documentation/iPLM/pgs/libraryfolder.html
There really is no reason for the vast majority of users to ever open their iPhoto library folder. That includes me!