Well, it's highly unlikely you will find someone who looks exactly like you, that is a complete stranger (but it seems to happen in those Mary-Kate & Ashley Olsen movies...
). The computer recognizes that you have one of the NPC portraits, and changes it to be certain you don't have two identical characters. I usually choose Keldorn's portrait when playing a Paladin, and the computer gives him the 'Bald-headed brute' portrait (first one on the BG1 list).