Now we have our first solid bit of evidence HomePods firmware shows support for infrared face unlock in the BiometricKit. This is similar to what Lumias and Galaxys use and works in low light.
Also hidden in the firmware is a graphic representation of the device a bezel-less phone with a characteristic cutout on top, which will hold the selfie camera and likely the facial recognition hardware. Theres just enough screen left to the sides of the cutout to show basic status information.
The facial recognition tech is dubbed Pearl ID while the phone is called just D22. Apple will likely keep a fingerprint reader on the iPhone 8, perhaps on the back or on the power button as the facial recognition weve seen so far has been slower that the lightning reflexes (0.1s or so) of a fingerprint reader.