Whenever you import pictures into iPhoto, the program makes copies of your photos, always leaving your original files untouched.
When you import from a camera, iPhoto leaves the photos right where they are on its memory card (unless you use the “Erase” option).
When you import from the hard drive, iPhoto leaves the originals in whichever folders they’re in. As a result, transferring photos from your hard drive into iPhoto more than doubles the amount of disk space they take up. In other words, importing 1 GB of photos requires an additional 1 GB of disk space, because you’ll end up with two copies of each file—the original, and iPhoto’s copy of the photo. In addition, iPhoto creates a separate thumbnail version of each picture, consuming about another 10 K to 20 K per photo.
iPhoto stores its copies of your pictures in ...