iPhoto includes built-in protection against overzealous editing—a feature that can save you much grief. If you end up cropping a photo too much, or cranking up the brightness of a picture until it seems washed out, or accidentally turning someone’s lips black with the Red-Eye tool, you can undo all your edits at once with the Revert to Original command. Revert to Original strips away every change you’ve ever made since the picture arrived from the camera. It leaves you with your original, unedited photo.
The secret of the Revert to Original command: Whenever you use any editing tools, iPhoto—without prompting and without informing you—instantly makes a duplicate of your original file. With an original version safely tucked away, iPhoto lets you go wild on the copy. You can remain secure in the knowledge that in a pinch, iPhoto can always restore an image to the state it was in when you first imported it.
The unedited originals are stored in an Originals folder inside the photo folder for each date, deep in your Home → Pictures → iPhoto Library folder. (The Originals folder doesn’t exist until you edit at least one photo.)
To restore an original photo, undoing all cropping, rotation, brightness adjustments, and so on, select a thumbnail of an edited photo or open the photo in Edit mode. Then choose File → Revert to Original. iPhoto swaps in the original version of the photo—and you’re back where you started.
As noted earlier, iPhoto does its automatic backup ...