Here is a demo of the Face Unlock app, Facelock for Nokia N9. This isn’t new to Nokias – at least 2 Nokia Worlds ago I remember this app winning the dev contest for this idea and implementation.
I’m not sure how this will work with pictures, if like ICS on Android it might be fooled with a photo.
You have to swipe away the N9 lock screen first and then this facelock screen appears. The Android version has the face unlocker bit as soon as you press the lock screen which is good but then it obscures the information that you might want to read just by pressing the lock button (and not necessarily wanting to unlock the phone).