Go to "User CP" in the blue bar just under where it lists the thread you are viewing and what not. From there, go to edit avatar and select "Use Custom Avatar" and either enter the URL of the pic or the location on your PC. Be aware, there are size restrictions, under 75x75 or 15.6 kbs, whichever is smaller.
I do pity whoever is next in line and that was a serious statement.
That person can toss posting as part of the community right out the window and instead spend all his/her time here tending garden then being called out for accidently pulling up a couple of flowers in the handfull of weeds