Look at the throat patch, the whiteness (or lack of) on the inside of the legs., the white ring around the eyes. Many of these things vary from deer to deer. I have a buck on my property that should be 3.5-4.5 this year. He has very, very dark hair along the front of his rear legs. He also has a white spot on the front of his heel of his front right leg.

Trail camera photos really does help spot these odd characteristics.

I also look for ear tears, and body scars. It certainly is easier with bucks versus does, but occasionally you can tell your looking a familiar doe too.