See the [color:"red"]My Home[/color] link at the top.
Click on it.
See Main configuration.
Click on the [color:"yellow"]edit[/color], right from Personal information, email, password, etc.
There's an empty box where you write your signature.
Near the bottom is a space where you write URl to your pic.
URL to your picture (80x80 max pixels, may be smaller) (.gif, .jpg, .png accepted)