My wife has this, and has often said if I didn't approach her for the second time after we met she would never have been able to find me again. Once she/we figured out it was a thing about 5 years into dating, some things got a lot easier.
We found out her dislike of certain movies (think Memento or Pulp Fiction or Snatch) was because she couldn't tell the characters apart enough to follow the plot. With me narrating or with closed captions that denote who is speaking, it goes a lot smoother.
She used to wonder how anyone could go to a spouse's friend's gathering where you don't know everyone, like an extended family wedding or something, because there is no way she could learn everyone's voice quickly enough to recognize them, and couldn't understand how everyone else apparently did. She just had no idea that you were supposed to recognize people by face.
Like someone said, she is also great at recognizing horses, cats and dogs. Zero doubt there. But cars she cannot recognize at all when the colors are different. She has read articles that this is related, ad most people tend to recognize cars the same way they do faces, with headlights, grill, hood, mirrors automatically registering as a 'face' in the human brain or something. So since her brain doesn't do that, all she's got to go on is 'blue'.
What is interesting is that she says she primarily uses voice, plus hair and gait and things like that to recognize people, but pretty much cannot recognize without the voice aspect. On the other hand I can easily recognize someone a hundred yards away, walking away from me, by hair and stride. I can't fathom perpetually not knowing who is around me. This comes up a lot as we live in a small town and when some stranger starts chatting you up in line at the grocery store and your 3-year old has to tell you "mommy that's ian from our street" before you have any idea who you are talking to, it is a little awkward.
Also her best friends from high school are all the unique looking ones. In a private high school class full of blond yuppies, my wife befriended the black girl, the short-haired lesbian, the frizzy haired redhead, the incredibly pale redhead and the half-asian. And they are an inseparable friend group to this day, 12 years later. She has openly said (to me) that the reason she gravitated to them in the first place is because she could recognize them. And she introduced them to each other. Amazing how such a thing shapes your life, or many lives.
It is hereditary. Her dad has it, we believe her half brother has it due to a few drunken conversations but he wouldn't admit it. And we are fairly convinced 1 of his 3 kids has it after spending a weeklong vacation with a large group (so multiple middle aged aunts, grandmas, a nanny, friends parents, etc). More than a few times the poor kid would ask a sibling where mommy was when she was in the room, and a few times he'd approach a relative and do a double take when they spoke, then go looking for his mother - sometimes with another failed attempt or two along the way. Things kids do, sure...but there's something different about it. When you see it, you can tell he can't figure out who is who all the time, and is otherwise a very bright kid.
Thankfully our daughter is fine. My wife has been able to use her to find me in public since she was like 18 months old. She's a very handy tool. Also for finding my car - say wife is supposed to drop something off in my car while I am at work, if I didn't drive the Miata that day her choices to find my car are either read the license plate on every grey one, or she can ask our daughter "where's baba's car?" and she'll point it right out. And the car is a dark grey bugeye wagon with very dark tint and gold wheels. Not very hard to find in a sea of silver camry and accord sedans.