Ignoring the ethics of if we should be using facial recognition in the first place (that’s a whole other discussion)…
Colors (is it as reliable for people of different skin tones?)
Colors (is it still reliable if a pasty-white me went out and spray tanned myself orange?)
Colors (How about if I put on make-up?)
Colors (How about if someone of a different skin tone put on make-up?)
Colors (If the light level in the room was darker / brighter, how would that affect the results?)
… And how similar would someone need to be to trigger a match? … Children might fall into the “close enough” category, and depending on the application, it might not be good enough. Identical twins would definitely be a match, and there are a lot of twins out there. Is there something to prevent a twin from imposing on the other twin’s privacy?
… And what if I looked at the camera from different angles. Would it still match me as me? or would I be someone else?
… And the people from the previous cases, would they still be identifiable?
If someone’s eyes are open, closed, red from lack of sleep?
Do they have a rash or a new injury?
Are they in the middle of talk-like-a-pirate day and have an eye patch?
Do they have a new collection of facial hair?