Gravatar is a very useful service but can cause some minor privacy risks if you are not fully aware of how the service works. Anyone (or any site/service) that knows your email address can retrieve and publish your Gravatar.
If you want an avatar that is only used on able2know, I would suggest using an email address that is only used for able2know. If you use Gmail, this is relatively easy as you can create aliases for your Gmail address. For example, you could use [email protected]
for your able2know account and if you then created a Gravatar for [email protected]
and didn't use it anywhere else, it would only be used on able2know.