Interesting article states this but I'm sure Apple researched and experimented well enough to solve the issues hopefully:
C. Challenges
The use of IR images for AFR is not void of its problems
and challenges. For example, MWIR and LWIR images are
sensitive to the environmental temperature, as well as the
emotional, physical and health condition of the subject. They
are also affected by alcohol intake. Another potential problem
is that eyeglasses are opaque to the greater part of the IR
spectrum (LWIR, MWIR and SWIR) [16]. This means that a
large portion of the face wearing eyeglasses may be occluded,
causing the loss of important discriminative information. Un-
surprisingly, each of the aforementioned challenges has led
to and motivated a new research direction. Some researchers
have suggested fusing the information from IR and visible
modalities as a possible solution to the problem posed by
the opaqueness of eyeglasses [17]. Others have described
methods which use IR images to extract a range of invariant
features such as facial vascular networks [14] or blood
perfusion data [18] in order to overcome the temperature
dependency of thermal appearance.
Another consideration of interest pertains to the impact of
sunlight if recognition is performed outdoors and during day-
time. Although invariant to the changes in the illumination
by visible light itself (by definition), the IR “appearance” in
the NIR and SWIR sub-bands is affected by sunlight which
has significant spectral components at the corresponding
wavelengths. This is one of the key reasons why NIR and
SWIR based systems which perform well indoors struggle
when applied outdoors [19].
https://www.google.com/url?sa=t&sou...ggyMAQ&usg=AFQjCNHkox4Zb5iz2jB3f18sdQC5CKjLiA
Wondering what will happen to the alcoholics?
If Touch ID under the screen was the original biometric idea, I wonder what will we see in the next coming months on Face ID that made Apple not want to use it at first.