https://www.theverge.com/2017/9/27/16373710/face-id-iphone-x-apple-facial-recognition-impostor

Today, Apple published a newly refreshed privacy page. With it came the most new information the company has released on Face ID since the iPhone X was announced. The details come from a new support page and a technical white paper on Face ID security, mentioned during the keynote and currently live on Apple.com. Over the course of six pages, the paper walks through the various privacy and security measures built into the new facial recognition system, including crucial details on how the new system works and how it will hold up under pressure.

The most detailed information comes from the description of how the iPhone X stores faceprints. In broad strokes, Face ID works the same way Touch ID did: the system reads your face (or fingerprint), then creates a partial version to compare against future prints. It’s a purposefully incomplete picture, so even if you could extract the data, it would be impossible to fully reconstruct a person’s face. According to the white paper, there’s also a random element to which information is retained, making it even harder to predict and spoof the system.