the tech isn’t perfect. Your iPhone X might not always unlock; a cop might arrest the wrong person. In order for software to always recognize your face as you, an entire sequence of algorithms has to work. First, the software has to be able to determine whether an image has a face in it at all. If you’re a cop trying to find a missing kid in a photo of a crowd, you might want the software to sort the faces by age. And ultimately, you need an algorithm that can compare each face with another photo in a database, perhaps with different lighting and at a different angle, and determine whether they’re the same person.