iPhoto Photos you import into iPhoto are saved in the iPhoto Library folder, located in the Pictures folder on your computer.
If a photo file becomes corrupted or is missing, you see the missing photo indicator—a solid black box—instead of the photo.
To find or replace a missing photo:
If you imported the photo from your hard disk, a CD or DVD, or a memory card—or if it’s still saved in your digital camera—just import it into iPhoto again (see Import photos from your hard disk or other computers).
Otherwise, try the following:
Click your computer’s Trash icon (not the iPhoto Trash icon in the Source list) and see if the photo is there.
Do a search of all your files and folders. In the Finder, choose File > Find, and then enter a search term in the search field.
When you find the photo file, save a copy to your desktop, and then import it back into iPhoto from there.
WARNING: To avoid permanently deleting or corrupting your iPhoto library, do not attempt to alter the contents of the iPhoto Library folder in your Pictures folder.