Is it possible for people with face blindness / prosopagnosia to draw other people (whose faces they cannot recognize) such that non-face-blind people can recognize the people being drawn ?
According to Bruce & Young model (1986), face recognition is composed of 2 main sub-processes, one more "perceptive" (called structural encoding) and the other one more "associative" (fru, pin, name generation). Bruce & Young model
A person with "apperceptive prosopagnosia" cannot create a precise percept, that is a mental representation of who he's looking at. He's unlikely to be able to draw other people face.
A person with "associative prosopagnosia" can create a percept of who he sees, but he cannot understand who the person is, deficit is semantic not perceptive. In this case, he is able to draw other people face, even though he cannot recognize it.
This subdivision can be found also in object recognition process and its related impairments: apperceptive agnosia and associative agnosia.
It's important to note that all this stuff is heavily theoretical. Reality is much more complex and sometimes unclear.
Apparently at least some are able to portrait people realistically, some like Chuck Close even photorealistically:
One of the weirdest things about all of this is that I’m an artist—a pretty good artist—and when I draw a portrait, it looks like that person’s face. So I’m clearly able to see distances and features the way I would on an inanimate object. But for some reason, the “recognition” part of facial recognition in my brain is broken.
Unfortunately, the linked GeoCities image of the drawing seems to be unavailable, at least not on archive.org and the GeoCities mirrors I consulted.
I draw really well, even though I can't necessarily remember a face. Drawing it helps. [...]
My life drawings don't emphasize the face, though, and what I usually do with a face is the significant gestures of the nose, eyebrows, and mouth, rather than a full rendering. I would hate to do a lot of portraits. My flower portraits, however, are right on!
This post also seems to indicate that drawing other people might help face-blind people to better / more quickly recognize characteristic facial features by training observation skills (assumption mine) although the author admits to struggle with considering all features as I understand it.
CHUCK CLOSE: Yes. I have a great deal of difficulty recognizing faces, especially if I haven’t — if I have just met somebody, I — I — it’s hopeless. I will never remember them again, unless it’s reinforced over and over and over.