iPhoto Libraries
When you upload your photos into iPhoto, they are stored in a library folder where the software organizes and keeps track of their precise locations. Certain data files are also created to help in their organization. These are also stored in the same folder as the photos.
When working with iPhoto, you do not actually go into the library folder itself. Instead, you simply use the software's interface. Nonetheless, it may be useful to understand how the things in the library folder work, especially when you encounter some problems with iPhoto. Following are a few of the files or folders you will find in the library.
Library Folders and Subfolders
iPhoto 5 and earlier versions store the photos in the library folder itself. In later versions, this folder contains subfolders categorized by year. The year folder contains subfolders classified by month, which in turn is classified into 31 subfolders for each day of the month. The actual photos are contained in the "day" subfolder.
AlbumData2.xml
This folder is created by iPhoto 8 and later editions. It stores data on the albums and events in the library folder but not the photos themselves. A program that only needs a list of the stored albums and events will be able to run through this folder faster.
Cache
This folder, found in iPhoto 8 and later versions, contains additional data needed by the iPhoto library. These data are requisites for the proper operation of the library so it should not be deleted.
Contents/PkgInfo
This gives a type and creator code to the iPhoto 7 package to identify which application it belongs to.
face.db, face_blob.db
This folder contains data needed for the face recognition feature of iPhoto 8.
iPod Photo Cache
This is created by iTunes to sync your library with an iPod.
Library.Data
These files are named differently for the different editions of iPhoto, but they all refer to the central database where all information is stored.
Metadata Backup
This is an iPhoto 8-created file that stores backup metadata of your files stored in the library.