(..) The one relevant here is prosopagnosia, the inability to recognize people by their faces. A prosopagnosic can't recognize friends or family members unless they say something; he can't even identify his own face in a photograph. It's not a cognitive or perceptual problem; prosopagnosics can identify people by their hairstyle, clothing, perfume, even the way they walk. The deficit is restricted purely to faces.

(Ted Chiang "Liking What You See: A Documentary")