I don't know about real outlaws in the Old West, but the ones in films often wore a mask; typically a bananda, often fancy, that covered their mouth and nose. This was the badge that showed they were baddies. But could it really have prevented them being identified, the reason given for their wearing masks?
Probably, yes. I've just put on a surgical mask and tested my iPhone. It didn't recognise my face. Amazingly, the phone hadn't been confused in the least bit by my radical beard trim, done some weeks back, for reasons of hygiene. But this is different. My phone didn't know me any more. I could still tap in the passcode of course.
Not all Western outlaws wore bandanas; there was a second popular style: the black mask around the eyes, like Zorro or the Lone Ranger.
Whether Style 2 affects the iPhone facial
recognition or not I don't know yet. My prediction is the impact will be less than for Style 1. I've bought a Zorro mask online and will be able to
report further, sometime towards the end of next week.