The face is a constant flow of facial expressions. We react and emote to external stimuli all the time. And it is exactly this flow of expressions that is the observable window to our inner self. Our emotions, our intentions, attitudes, moods. Why is this important? Because we can use it in a very wide variety of applications.
With measurement comes the power to categorize and control. These are technologies that enable us to be judged at a distance, to be identified as a threat or a sales opportunity just by the way we look. Facial recognition takes this further. Not only can we be reduced to a set of externally-verifiable measurements, but these measurements are assumed to somehow constitute our identity.