I don't know if being banned removes the avatar but if it does, you could ask a friendly Mod to ban you and I THINK you'd need to use another e-mail address to register and use another username.
So is it a once and forever grab that stays on answerbank until you change it ....its surely worth changing or deleting the exsiting gravitar one...unless that ones still essential for another site
Catterpillars done what we suggested I think wolf,,, as the avatare on there profile is now showing a caterpillar rather the personal photo what was there before
Following your suggestions I found that the pic was grabbed from gravitar - an old pic from a long deleted WordPress account which I'd forgotten.
I didn't know I had a gravitas account!
Finally managed to sign in and change the pic so problem now solved.