The first time my dog saw me wearing a hunters-orange cap, he started growling like he'd cornered an intruder. When I took off my hat and told him to shut up, he figured out it was me. :) (Fortunatly he was in his crate at the time, or me may very well have bitten me -- he really did think I was a stranger prancing about "his" house.) Dog's use vision to recognize people too.