Chinese cops are using facial-recognition sunglasses. Here's how that tech works.

Software that powers facial recognition generally uses a two-step process, says David Alexander Forsyth, an artificial intelligence expert and chair of computer science at the University of Illinois at Urbana-Champaign. Step one is to figure out where the faces are in the image in question; the system is looking for a window-like section of the image that also has someone's countenance in it, and not the other stuff of modern life, like stop signs and cars. Step two: it needs to see if it can match the face to any in its database. "Turns out, that's a harder problem," Forsyth says, in comparison to step one. "People tend to look like each other."