I have prosopagnosia so it takes me ages to recognize people at all. If I've seen people A LOT I can recognize them everywhere. Otherwise I only know them because I understand they know me. When I'm with new people, I recognize them mainly by clothes and hair styles. It goes weird if they remove a jacket and "disappear"!

I do well with tests for prosopagnosia if the photos are identical, then I remember the photo itself, or if the people have hair. I'm completely lost with tests where hair is removed. I was showed 10 famous people and I only recognized one, Muhammad Ali the boxer. It came out that really was prez Obama..... LOL.