The contents of your iPhoto library have been stored as a package file since iPhoto ’08. Previously, the iPhoto library was simply a folder you could browse like any other. Apple’s decision to make it a package was a good one in my opinion as it led to less user-initiated library corruption and lets the operating system treat the iPhoto library as a single file rather than a folder. That’s especially helpful when you consider that it could potentially hold over a hundred thousand items in it!
However, iPhoto still seems to corrupt its own library by itself occasionally. If you find question marks where you photos used to be, thumbnails that don’t correspond with the right image or don’t correspond with any images at all, you might be the victim of iPhoto library corruption. If this happens, you’re going to want to take the steps listed here to begin repairing and rebuilding the library. Note: This can be a time-intensive process — especially if the library is large.
After you’ve gone through each step, check the library to see if your corruption issues are resolved. If they remain, I recommend taking a look at iPhoto Library Manager, available for free here. This can be used to continue your corruption-resolving project, but also has features that you can pay for as well. Two of the most popular are duplicate removal and the ability to merge libraries. And, as Jason Hyerstay would tell you, iPhoto Library Manager has one of the cutest icons he’s ever seen. (Ed. Note: LOL. -KH)