According to Mark Gurman at 9to5Mac, Apple has added face detection API in iOS 5. Apple had previously used face detection on the Mac for everything from iPhoto's Faces feature to OS X Lion's advanced PhotoBooth effects, and along the way bought the company behind it, Polar Rose.
We have taken a look at these iOS 5-exclusive APIs and they are highly sophisticated. The first, called CIFaceFeature, can determine through an image where a person’s mouth and eyes are located. The second API, CIDetector, is a resource within the operating system that processes images for face detection.
So while we might see the built in iOS PhotoBooth get the same feature boost as Lion, we could also see other novelty apps, and games, and perhaps one day facial recognition for security. ("Oh, hi Steve. Unlocking your passwords now.")