Windows 8 will feature expect picture passwords one of the security features on the operating system. So what is picture password? Picture password will allow user to select an image of his/her choice and then draw out any gestures to help authenticate legitimate users. The user can draw lines,circles or even tap on any area of the image.
So its simple- select an image- choose an secret gesture and you are done.
You can find more details and also complete working logic of this system at Microsoft’s Blog.