刷 'to swipe / scan' + 脸 'face' - built on the same 刷 used in 刷卡 'to swipe a card'. Just as a card is swiped, now the face is scanned.
culture
Facial recognition has become routine in mainland China for payments, entering housing compounds, boarding trains, and even unlocking vending machines. 刷脸 captures this ordinary, everyday verb for it.