iPhoto creates its entire directory structure in the Pictures folder inside your user folder, starting with a folder called iPhoto Library. Inside it, iPhoto creates three special folders: Originals, Modified, and Data. Inside each are folders for years; inside those are folders corresponding to film rolls, and inside those film roll folders you finally get to the actual image files (Figure 2.16).
Figure 2.16. iPhoto uses a film roll-based directory structure that starts in your Pictures folder.
The top-level Originals folder contains your original photos. The Modified folder contains, in its film roll folders, modified versions of your photos. Until you make a change to an original image, there won't be a corresponding file in the Modified folder. The Data folder holds thumbnail images of your photos; they look the same in the Finder's preview, but are much smaller in size.
Other than the items mentioned in "Old Stuff That Can Go," do not move, rename, or delete anything inside the iPhoto Library folder in the Finder because you'll risk confusing iPhoto and corrupting your library!
If you ever have to recover your photos from a corrupted iPhoto Library folder, look in the Originals and Modified folders. Originals contains the photos as you imported them and Modified contains the versions that you edited.
To locate a file corresponding to a photo in iPhoto, -click it in iPhoto and choose Show File. If you have edited the file, you can instead choose Show Original File to display the original file in the Finder.
Old Stuff That Can Go
Although you shouldn't mess with files and folders in the iPhoto Library folder generally, there are a few items you can delete without harmif they're presentbecause they're relics from previous versions and are no longer used. You likely won't save much disk space by deleting these unused items, but sometimes it's nice to have things be a bit more tidy.
With iPhoto 6, the structure of the iPhoto Library folder changed significantly. Previous versions of iPhoto used a year/month/day hierarchy of folders, storing originals and modified images separately within the final day folder. If there were errors in upgrading your library when you first launched iPhoto 6, those year folders may still exist at the top level. As long as you allowed iPhoto 6 to recover the photos nested inside, you can delete all the year folders with impunity (it's worth checking inside each one first, of course!).
Other items you can delete include the Desktop, iDVD, and Screen Effects folders. These folders merely contain aliases used by previous versions of iPhoto for your Desktop picture, iDVD, and the Mac OS X screen saver.