If you've uploaded an image to Gravatar, and it's not appearing here, the usual reasons for that problem include:
(a) using the wrong email address to register on Gravatar. (It MUST be the same one that you used to register on AB, as that's the only way that your avatar can be linked to your account here) ;
(b) failing to activate your avatar in your AB account settings. (Click 'View your profile', then 'Edit My Profile' and make sure that there's a tick in the 'Your avatar is currently active' box at the top of the page) ;
(c) failing to give your avatar a 'G' rating on Gravatar. I've never had this problem myself; indeed, I can't even recall being asked to 'rate' my avatar at all but some ABers have stated that it's necessary to to give your avatar a 'G' rating in order for it to appear here. (Gravatar uses the US film classification system to rate avatars, with 'G',for 'General', being their equivalent of our 'U', for 'Universal').