Appearance do matter, just not a lot online. If you think bad of fat people in RL then you will probably think bad about people who are fat on the internet, but you'll be much more inclinded to not pay as much attention to it as you would in RL.
But honestly you should stay away from posting pictures of yourself on the internet to people you don't know in RL, nobody really thinks less of you if they can't see you so it's lose/lose really imo.