Prosopagnosia aka Face Blindness is the inability to recognize the faces of familiar people.
(It comes from the Greek: "prosopon" = "face", "agnosia" = "inabilty to recognise/identify familiar people or objects". In severe cases people are unable to recognise their own family. Two per cent of the UK population suffers from some form of face blindness, and as someone who is "not good with faces" I think I might be one of them. But now, when I can't put a name to the face, I can at least put a name to the condition.)