Prosopagnosia is an impairment of one's ability to recognize faces. This interview with one person with face-blindness is fascinating top to bottom.

What problems does it cause?
The issue is how I remember faces. It doesn’t matter if I know the person: I’ve walked right past my husband, my own mother, my daughter, my son, without being able to recognize them.
It can be very embarrassing, and it can offend people. I once had to drop a sociology class, because I told the professor, to her face, that she was a horrible lecturer. I thought I was complaining to a fellow student! It’s as if I have a missing chip — you feel like you’re just not trying hard enough. Faces are so important to humans that we have a special part of our brain dedicated to recognizing them. Most people remember them as a whole piece, but I don’t.
To tell people apart I have to find a distinguishing feature. And context is huge. If I’m expecting to see somebody, I’ll figure out who they are by observing their body language, listening to their voice. Good-looking people are the most difficult to recognize.
Is that because their faces are symmetrical?
Yes! Straight teeth, noses within regular limits … everything is so … normal! It’s like a flock of chickens. So what I do is look for specific features. I have one friend who’s average height, middle aged, and white, and she works in an office full of average middle-aged white ladies. And even worse, it’s a doctor’s office, so they are all wearing scrubs. If I meet her at work, I can only recognize her if she smiles — it’s very specific. But these are the things I look for: Some people have a distinctive nose; some people have two different-colored eyes.

I had no idea Chuck Close suffered from prosopagnosia, and now I see so much of his work in a new light.

This is one area where some technology like Google Glasses could really help.

I have problems watching a lot of films and TV shows because everyone looks so perfect I can’t follow the plot. I have a face-blind friend who used to work at the Beverly Hills Whole Foods. His employers loved him because he never recognized the famous customers.
Can you recognize yourself?
Not always. I’ve had to say to friends of mine, “Is that a picture of me? Who is that?” If I unexpectedly see myself in a mirror, I might think it's somebody else. It's like, Why is that woman staring at me? Those times, I’ve been struck by how serious I look.

One of the many interesting ideas to come from this piece is that prosopagnosia can also be seen as a positive, as immunity against our obsession with symmetry as an indicator of attractiveness, or to unconscious racism.

What attracts you to people?
I have a thing for voices and intelligence. While I can appreciate that someone is attractive on an aesthetic level, I don't feel it on that visceral, "Whoa! They're hot!" way. At least not when I first meet them. I really only become sexually interested when I have talked to someone long enough to know them. I would be hard work to date. I met my husband at the university science fiction club. He has an incredible voice — he’s a public speaker, his grandfather was a radio announcer, and his father works in television. And he’s the smartest person I know — he used to teach English literature.