But, if we are comparing the brain to a computer, can't the brain use a random-face-generator method? =P

That nullifies the need to remember a thousand faces--you'd just need to know what qualifies as a face!

Conjuring a crowd shouldn't be any different than conjuring a single person. It's the same thing, but there's a lot of them. If we're comparing ourselves to computers, creating a couple thousand faces is easy. And now for proofless conjecture: Especially easy if, when the faces aren't being noticed, they blurr out. I bet the faces in crowds change if you look at them twice, much like text.