iPhoto includes a feature that allows you to rebuild the currently selected iPhoto library.
Sometimes rebuilding the library may resolve issues such as the library appearing to be unreadable, missing photos, or other issues related to reading the iPhoto library structure.
Note: This article is for iPhoto versions 6 and later.
Important: You should back up your existing iPhoto Library folder before using the rebuild feature. A backup allows you to restore the iPhoto Library if anything unexpected happens during the rebuild that prevents the library from rebuilding correctly.
Before performing a rebuild, you should install any iPhoto updates by using Software Update.
If a software update resolves your issue, then you don't need to rebuild.
To rebuild the iPhoto library: