For some reason my iPhoto suddenly reported "damaged" when it HAD been working for over a year.
The solution for me was to delete iPhoto (right-click or control-click, and select Move to Trash. Then I went to the Applications/Utilities folder and started up Terminal so that I could enter the
sudo find /var/db/receipts -iname "*iphoto*" -delete
command mentioned above. Finally, under the Apple menu (the Apple icon in the top-left corner of the screen), I opened the App Store, and in the App Store I selected Purchased, where it showed that I could install iPhoto.
Once that install was completed I could open iPhoto on my computer and I had full access to my entire photo collection.