You'd be surprised / scared / outraged if you knew how common this is. Any time you've been in a public place for the past few years, you've likely been watched, analysed and optimised for. Advertising in the physical world is just as scummy as it's online equivalent.

Check out the video here http://sightcorp.com/ for an ultra creepy overview. You can even try their live demo: https://face-api.sightcorp.com/demo_basic/.