It's a CBP-operated system called Biometric Exit, and from what I've heard is being rolled out at other airports, including Boston [1], San Jose [2], and Orlando [3]. So it's not exclusive to Delta or ATL... though this might be the largest deployment so far.
[1]: https://www.airportfacescans.com/
[2]: https://www.mercurynews.com/2018/08/06/san-jose-airport-show...
[3]: https://www.futuretravelexperience.com/2018/08/five-examples...