Photos is the Apple photo management app replacement for the now unavailable iPhoto app, and it shipped with OS X Yosemite 10.10.3. If you’re experiencing a crashing app at launch, failed imports, or thumbnails or photos missing, then you may want to try repairing your Photos library to recover from these errors. Before continuing, you should ensure that you have a backup of your library via Time Machine or manual copying to another location.
Follow these steps to recover your Photos library:
1. If opened, close the Photos app
2. Relaunch the Photos app while holding the Command + Option keys
3. The “Repair Library” dialog will appear asking if you’d like to repair the library
4. Select “Repair”
After doing these steps, the Photos window will change to a “Repairing Library” view with a progress bar indicating the current state of repair. Depending on how much content you have in your library, this process can take quite a while as it rebuilds and repairs the library on your Mac.
This process will only repair the default Photos library on your Mac. If you have multiple libraries, you will need to switch to the one needing repair before performing these steps.