Well honestly there doesn't seem to be many native Cantonese speakers on the site. At the moment there are around 90 requests but only 14 recordings have been made. Hopefully more native Cantonese speakers will join the site.
On the other hand if you are learning Japanese or Mandarin I think there are are a lot of native speakers of both languages.
I think the avatars only show up at the comments section and not here in the forum.
All you have to do is go to http://www.gravatar.com and sign up using the e-mail address you used to sign up for CantoneseClass101.com. Then I think you the picture you choose as your avatar will be available for use at any website or forum you signed up with using the same e-mail address.