Apple has released a small update to iPhoto, which addresses a couple of small issues that users of the program have been experiencing with the face-recognition technologies in version 8 of the program.
While face recognition has been welcomed by many, the last update to iPhoto introduced a few problems with the ability to find faces, leaving many blank. Apple has recognized this and has addressed this problem in the current update.
For people who have been running iPhoto 8.1, this update requires an extra step for detecting missing faces. You will need to select all the previously imported photos, right-click them, and then select "Detect Missing Faces" in order to re-detect the faces in those photos.
The 12MB update should be available through Software Update, and is also available for download at Apple's support website: http://support.apple.com/kb/DL970
The update requires OS X 10.5.6 or later and also that you have version 8.1 already installed. For more information on this update, check out this KB document: http://support.apple.com/kb/HT3941