how many different human faces can the brain recognize and remember?

I think it depends on the brain.

Some people cannot remember any – it is a disorder called prosopagnosia.
http://en.wikipedia.org/wiki/Prosopagnosia

I believe the answer for the average person is in the thousands.

A quick tally of the faces I know includes my family (~40), people from my hometown (~600), people from college (~2000), and people I recognize from living in San Francisco (~600). I’m including people I interact with minimally (the mailman, the barista at my favorite coffee shop) as well as people I see regularly but never interact with (the people in my office building’s elevator, the shoe shine man I pass on my way into the office).

Then there are the faces of people that I recognize despite having never seen them in person: historical figures, politicians, athletes, actors, authors, musicians, and other newsmakers. Looking at a list of celebrities born today, I’d guess the average person would recognize at least 4 of them. Assuming that today is typical in that regard, the average person would recognize at least 1,460 famous faces. In addition to these stars, there are also less famous people that we recognize (all the actors in our favorite television series, all the players on our favorite sports team).

I’d guess my personal total is above 5,000.

If the word “recognize” is taken to mean “distinguish between”, the answer is upwards of millions. We’re highly adapted to note very small differences in facial features. There’s a genetically finite number of human faces (in the hundreds of millions), but that’s before you include the variation caused by culture and nurture.

As for “remember”, that’s much more variable based on the individual. The numbers are likely to be far higher than Sferik guesses, because 99% of the faces you recognize will be at an unconscious level—if only to classify them as “strangers”. You’re doing this all the time, and considering how many people, whom you never speak to, eventually get classified as “locals I see repeatedly”, that’s quite a lot of recognizing going on. I suspect that including the faces that you memorize from the media, most of us are hitting high six figures.

The question I was considering was this: If I saw a person’s mugshot and was then asked if I recognized that person, I would be able to say something like, “Yeah, that’s the guy from the local delicatessen.”

I also considered the reverse question: If a sketch artist asked me to describe the guy from the local delicatessen, would I be able to articulate distinguishing facial features?

I’m pretty sure that by these criteria, my personal limit tops out in the thousands.

I didn’t include people who I subconsciously “classify as strangers” but whose facial characteristics I forget just moments later. I suppose it depends on the size of the city I live in (San Francisco) and how long I’ve lived there (2 years), but there are a relatively small number of “locals I see repeatedly,” at least not that I remember.

With each new day, I probably add a few new faces to my memory bank, but I also have forgotten many of the faces I that I would recognize a few years ago. I concede that “above 5,000” may have been a conservative estimate but “high six figures” sounds high to me.

I don’t know if this is connected to the same part of the brain that visual recognition uses, but I have always been amazed at how many voices we recognize. You’ll be listening to radio commercials and be able to instantly tell what actor is voicing the commercial. I wonder how many voices we recognize as well.

I have a bit of trouble discerning subtle facial emotions. I can read anger, sadness, and other extreme emotions, but many of the subtle ones I find hard to discern. Not sure why, my brain must be fucked up.