My wife is useless with faces. It takes her quite a few meetings with a person to be able to recognise them. When we watch films together I will often need to tell her that the person on screen is the same person we were watching earlier but is now wearing something different.
One day she told me that rather than concentrating on the actual people on screen she finds herself compelled to count irrelevant items in the picture - panels on the wall behind, beads on someone's necklace, glasses on a table. She can't believe that I don't do this too nor will she accept that this is an unusual thing to do.
Please tell me that you guys don't do this too.
Lastly, back on the faces, an example of this that blew me away is from Hot Fuzz. Don't read the rest of this paragraph if you haven't seen the film and don't want a great visual gag spoiled for you. At one point we see Bill Bailey (whom my wife has seen hundreds of times) as a desk clerk in a police station, at another we see him again at the desk but with a completely different hairstyle. Then to conclude the joke we see them side by side and realise they are twins. Not only had my wife not realised it was Bill Bailey on either occasion, she also says she didn't realise that there were two of him at the end - because their hair was different!