I'm a mild case, so most people don't notice in day-to-day interactions. Your average Hollywood actress looks like a clone.
Every day I have a "Is that Bob?" moment walking past people I haven't met. I'm quite reserved in saying "hi" to people I'm not 90% sure I know. A lot of people think I'm a friendly stranger because I wave, then a few second later think "whoops, not who I thought that was" when their reaction doesn't match Bob's.I almost never greet by name- it's always generic "Hi there" type, to cover if my first guess is wrong.
Yes, it's purely visual. When watching a movie, my wife can spot actors and say "isn't he from movie yadda?". Especially with actresses that change hair color, they become a totally different person.
Now voices, those I get. Once an actor speaks, I can often peg where I've heard them before. When actors have heavy makeup, I can spot people before she can.
Smells? I try not to hang around people with any smell (good or bad) at all. :)
Posture, walking gate, height are things I do consciously use. Actually, I sometimes have a better shot at identifying people from behind, (i.e. walking ahead of me), because there's no face to cause confusion.
Glasses & beards are great for short term, but they change long term. For business meetings & groups, clothing is the way to go. Red shirt is Bob, white shirt is Fred. The next day I have to pick up again by voice and forget the clothing identifiers.
I can recognize faces, but it takes hard concentration- enough that I often have to tune out what people are saying. With a couple folks, if I put in the effort, I can learn the quirks in their faces. (Big nostrils, gap tooth, etc). For a group of 10 people - forget it. I won't even try. Smile & nod time.