Face Ache

I think this bit of software is so fantastic - ok I haven't had time to try it out exhaustively but first impressions - very good.
"KeyLemon provides a new experience to access your computer.
Instead of typing your password, you just need to smile to the webcam and KeyLemon will recognize you.
It is fast, simple and convenient. So, start now and create your own and unique face model!"

I don't know quite how good/secure this software is but I installed it and 'enrolled' my face it seemed quite happy unlocking and locking my PC (though it is only a screen saver at the moment). This is an alpha version but it was able to recognise easily where on the video picture my face was, not that difficult a feat you might imagine by image recognition for computers has been a hard nut to crack.
Having unlocked the screen several times without incident I thought I need to try a different face - the easiest one to get hold of was my wife, I asked her to sit down in front of the camera and the screen didn't unlock - fantastic, not only can the software recognise my face it can differentiate between mine and my wifes (ok so not hard I'm bald she has long blonde hair). Try it out see what you think.
Link