What do each of the files do inside of an iPhoto Library?

Solution 1:

Basically, all the files like xml, db and such help different softwares like iPhoto, iMovies etc gain information about your photos.

Excerpted from Fat Cat Software: iPhoto Library Internals help page:

AlbumData.xml

This file is written out by iPhoto as a way for other applications (such as iMovie and iDVD) to be able to easily access the contents of your iPhoto library. You can read in more detail about this file here.

AlbumData2.xml

This file is only created by iPhoto 8. It is a smaller version of the AlbumData.xml file that only contains information for the library's albums and events, and none of the actual photos. This file is faster to read for programs that only need to get the list of albums and events in the library.

Attachments

This folder is used by iPhoto 9 as a temporary holding place for photos that are being sent using iPhoto's built-in email features.

Auto Import

This folder is created by iPhoto 7 and later. There does not seem to be any mention of this folder in iPhoto's documentation, but if you put some photos into it, then quit and reopen iPhoto, it will automatically import those photos into the iPhoto library and then delete them from the Auto Import folder. There is also an "auto import" Applescript command which does not appear to do anything when called. It's not clear if this was a planned feature for iPhoto 7 that ended up getting pulled out (but not completely, apparently), and it doesn't seem to be very useful for anything, especially since that folder is buried inside a package now, but that's what it does if anyone is curious.

Backup

If a library has been upgraded from an earlier version of iPhoto to iPhoto 9, a copy of the original database files from the library are stored in this folder before performing the upgrade.

Caches

Only present in iPhoto 8 or later, this folder contains additional data for the iPhoto library. Unlike some other Caches folders that can be safe to delete, this one is not, so don't go deleting it in an attempt to clear up disk space.

com.apple.iPhoto.plist

This file is actually not written out by iPhoto itself, but rather by iPhoto Library Manager. It is a copy of the preferences file that is associated with this library. When you switch between different iPhoto libraries, iPhoto Library Manager will swap out this preference file for the existing preferences before opening the library up.

Contents/PkgInfo

This is part of the new package structure in iPhoto 7 that gives the package a type and creator code so that the Finder knows what application the package belongs to.

face.db, face_blob.db

Contains the data for faces identified by the face recognition feature added in iPhoto 8.

iLifeShared

Starting in iPhoto 9, the AlbumData2.xml file is now stored within this folder rather than at the root level of the library package.

Info.plist

iPhoto 9 added this file, containing basic version information about the library

iPhoto.ipspot

This file is written out by iPhoto and read in by Spotlight in order to index the information about the photos in your photo library. You must have iPhoto 5.0.2 or later for this file to be present.

iPhotoLock.data

This file is used by iPhoto to help prevent more than one copy of iPhoto from accessing the library at one time.

iPod Photo Cache

This folder is created by iTunes if you choose to sync your iPhoto library with a photo capable iPod. It contains cached information about the last time the photos were synced and help speed up the syncing process, allowing iTunes to tell which photos have changed since the last sync and only update those ones. You can delete it if you want to clear up space, but iTunes will have to create it all over again the next time you sync your iPod's photos.

Library.data, Dir.data (iPhoto 2), Library.iPhoto, iPhoto.db (iPhoto 4, & 5), Library.iPhoto6 (iPhoto 6 & 7), iPhotoMain.db, iPhotoAux.db (iPhoto 8), Database (iPhoto 9)

These files/folders serve as the central database where iPhoto stores your library information. All your event, album, and photo metadata is stored in these files.

Data, Originals, and Modified

iPhoto 6 organizes its photos fairly differently that previous versions. Imported photos will initially be stored inside the "Originals" folder. Within that folder, photos are organized into subfolders based on the roll that they are in, so each roll gets its own folder. Those rolls are then sorted by date (2006, 2005, etc.) and put into dated folders accordingly. So, if you had a photo in a roll named "Vacation" and dated February 24, 2004, to find that photo, go into the "Originals" folder, then into "2004", then into the folder named "Vacation". When you edit a photo in iPhoto, the original stays where it is, and the edited photo is placed in the "Modified" folder, which has the same per-roll organization scheme within it as the "Originals" folder does. The "Data" folder contains all the scaled down thumbnail version of photos in your library. If you upgrade to iPhoto 6 from a previous version, iPhoto will rearrange all your photos from the old scheme into the new scheme. After upgrading, you may still see one or more leftover folders named "2004" and such. These folders should no longer contain any files being used by iPhoto 6, and can be disposed of safely.

Thumbnails, Masters, and Previews

iPhoto 9 organizes photos in much the same way as iPhoto 6-8, but uses the folder names Thumbnails, Masters, and Previews instead of Data, Originals, and Modified

Metadata Backup

Created by iPhoto 8, containing backup copies of the metadata for your photos, events, albums, and other library content. This information can be used by iPhoto to recover a library whose main database has been corrupted.

ProjectDBVersion.plist, Projects.db, Projects.db-journal, SharingActivity.db

These additional data files exist only in iPhoto 9 and contain information relating to "keepsake" items such as books and slideshows, and information for albums published on MobileMe, Flickr, or Facebook.

ThemeCache

A cache file used by iPhoto to store theme data used to make books, calendars, and cards

Thumb32Segment.data, Thumb64Segment.data, ThumbJPGSegment.data

In order to improve performance, when you add photos to your library, iPhoto creates small "thumbnail" versions of your photos and caches them in these files. In iPhoto 5 and earlier, these files are instead called Thumb32.data, Thumb64.data, and ThumbJPG.data.