Your iPhoto library is designed to hold up to 250,000 photos, depending on your computer’s memory and available hard disk space.
iPhoto stores your photo library in the iPhoto Library file, or “package,” in your Pictures folder (in your home folder on your hard disk). The package contains all the photos you’ve imported into iPhoto and any albums, slideshows, and projects (such as books, cards, or calendars) you’ve created using iPhoto.
WARNING: To avoid permanently deleting or corrupting your iPhoto library, do not attempt to alter the contents of the iPhoto Library package.
It’s a good idea to routinely back up your iPhoto library to a DVD or external hard disk so that you have a copy in case your photos become lost or corrupted for any reason.
To access your iPhoto library:
Click Events or Photos at the top of the Source list.
If you’re in full-screen view, click Events in the toolbar, or click Albums and then Photos.