When photos go missing from your iPhoto collection, it usually falls under two specific situations. You will need to work your way through both and figure out which one you are dealing with.
POSSIBLE ISSUE — When you launch your iPhoto application, and a message comes up saying that it can't find your iPhoto library file, or in the window, you don't see the name of your library file listed, then this tells you that iPhoto is having a problem finding your entire photo collection. In this case, you will need to give iPhotos a little help in finding it. Click this button to take you to the solution to this problem.
POSSIBLE ISSUE — Or, in the second situation, when you launch the iPhoto application, it seems to load your photo collection just fine. But the problem is a few, or maybe even many of your individual photos don't seem to be there anymore. If so, the article you are reading should help you to solve this, so continue reading on.
A Few Or Many of My Photos Are Missing
What's Causing This Problem:
It may not be known to you, but your iPhoto photo collection is more than just the iPhoto application stored in your Application folder.
All of your master photos, thumbnail and preview versions of your photos, and database records of how the iPhoto application handles all of your photos, are stored in a separate file (a folder really) that is in a completely different place on your hard drive from the main iPhoto application.
This separate file, called a “photo library” file, by default is stored inside of the pictures folder in your user folder.
Sometimes the database records become a little mixed up, and what the database shows as being correct doesn't match what's actually true with your master images stored with that database.
EXAMPLE:
A simple example of this might be that if you were to peek inside your folder full of master images, you might find you have 1,000 photos. But your database records might be off, and you only think you have 950. Launching the iPhoto application could cause problems and prevent those last 50 photos from being shown to you.
How We Can Fix This:
There are a few procedures that Apple has almost “secretly” written into the iPhoto application that will force it to “recalculate its math” and reconstruct its database.
In a repair procedure, it will go in and compare how many actual photos it finds in your library file to how many the database believes it has. If the numbers are off, it will fix this and “re-attach” to the ones it wasn't “aware” that it had before.
Additionally, if this repair procedure doesn't work, there is a “stronger” one that will actually rebuild your database.
Apple states on their support page:
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.
Repair Database
Checks for inconsistencies in your iPhoto library file and repairs them. Adds photos that are stored in the library but are currently missing from the database.
Rebuild Database
Examines and rebuilds your library. This should be used only when “repairing” the database doesn't work.
My Background Finding Missing Library Files:
Even though I have helped a lot of people with their missing iPhoto Photo Library files, I still have personally never experienced a corrupt or missing library file myself.
So, like I tell everyone that I help, I still can't give you first-hand knowledge of how to deal with your problem, since I've never even been able to reproduce the situation. And often, I never hear back from them, so I never find out exactly what fixed their particular problem.
But, what I can tell you from everything that I've heard from people with these problems, and from those that I have helped, is that in a few rare cases, iPhoto libraries seem to go missing during upgrades of iPhoto library files when a major version of iPhoto was just installed, and when their iPhone is connected to their computers and is doing various kinds of syncs and imports.
It's very strange. Coming from their stories, it's as if in these situations, when there is a problem, the software makes a decision to move the Library file somewhere else — possibly to the OSX trash bin!? And then iPhoto creates a whole new (and empty) library file. I, of course, easier not to believe all of this, but I've heard this story many times now, over and over, so I've had to accept that something strange is, in fact, going on.
Instructions
Backup your iPhoto library.
What you are about to do is a fix for problems like this written by Apple programming engineersand built and hidden away inside of your iPhoto application. In almost all cases, it's safe to run without ever causing any damage to your iPhoto library file.
But, for the safety of your photo collection, since there's a tiny chance something could go wrong with this procedure, please make sure you have a good backup of your library file. You can’t be too safe when it comes to your irreplaceable photo collection.
With iPhoto closed, press and hold down the option and command keys.
Launch iPhoto.
Don’t let go of those two keys until a special window pops up. The window will look different depending on which version of iPhoto you are running
From this new window, first, let's choose to repair your iPhoto Library Database.
It could take a little while if your library is massive
Relaunch iPhoto and look for your missing photos in the Events folders again. If you still can’t find them, repeat this process from step (2) but this time instead choose to rebuild the database from the list.
This also could take a little while if your library is massive
Relaunch iPhoto and look for your missing photos in the Events folders again.
This also could take a little while if your library is massive
Additional Information
Here’s the page on Apple’s website explaining this same process, including older versions of the iPhoto application: http://support.apple.com/kb/HT2638
Testimonials
Repair and Rebuild iPhoto using “iPhoto Library Manager”
If Apple's built in “First Aid” processes didn't restore your missing photos, it's possibly that the iPhoto application just isn't accessing, or isn't able to access, your library file with all of your photos in it.
By default, any time you launch the iPhoto application, it loads up the photo library file that was loaded when quitting out of the application last.
If you are trying to run Apple's first aid procedures to fix a photo library file that wasn't the one loaded the last time you launched iPhoto, or a library file that even the “first aid” part of the iPhoto application can't even seem to open (because it's so badly damaged), you may need to move on to a tool that will be more “powerful” and one you can specifically target at the correct library file you want to fix.
This tool is a third party piece of software — and really the only one out there of its kind as far as I can tell.
“iPhoto Library Manager” by Fatcat software is an application that does many things including the ability to merge 2 library files. But in particular, it offers “Rebuilding Corrupt Libraries.”
http://www.fatcatsoftware.com/iplm/
What I really like about Brian Webster’s approach is that his application doesn’t just try and fix your current “damaged” library, it instead (more safely) creates a completely new library file and pulls in all the photos and data it needs from your “damaged” one:
Sometimes, an iPhoto library will become corrupted, with missing photos, mysterious iPhoto hangs, or outright crashes. With iPhoto Library Manager, you can rebuild a new library based on your current library, starting with a fresh database free of corruption. You can even scavenge photos from the library that iPhoto may have lost track of.