Facebook already uses face recognition to recommend which friends to tag in your photos. The US government is in the process of building the world's largest cache of face-recognition data, with the goal of identifying every person in the country.
Walk up to the international check - in at a German airport, gaze up at a camera and walk into the country without ever needing to pull out a passport – your image is on file, the camera knows who you are.
Wander into a retail store and be greeted with personalised product suggestions – the store's network has a record of what you bought last time.
As the scale of face recognition grows, there's a chance that it could take its place in the technological landscape as seamlessly as the i Phone.
But to allow that to happen would mean ignoring the increasing danger that it will be misused.
Face-recognition systems have two components: an algorithm and a database.