See also here:
http://www.theanswerbank.co.uk/AB-Editors-Blog/Question925753.html
There are two places where people often go wrong with trying to get their own avatar to show up here, so I'll point those out to you now (so that you can avoid them):
1. The email address you use to register on the Gravatar/Wordpress site MUST be the same one that you've got registered with AB. It's the ONLY way that Gravatar can link your avatar to your AB account. Any other email address simply won't work ;
2. Gravatar will, I think, ask you to assign a 'rating' to your avatar. The ratings Gravatar uses are based upon those used in the USA for film certificates. You MUST choose a 'G' rating (i.e. 'General', equivalent to a British 'U' cinema certificate) for your avatar to be acceptable here.
BTW, you must be very cultured if you see AB's default avatar as 'chess pieces'; everyone else sees them as jelly babies ;-)