Most of the people who comment on here have done this, but a few haven’t, so I thought I’d remind people:
If you want your avatar to show up on wordpress blogs, nine times out of ten what you need is a gravatar account. It connnects your email address (hidden from viewers) with an avatar of your choice. As on other online networks you should use an image that is recognizable – either your brand, or a photograph.
This works for all WordPress blogs: self hosted or not. You can, if you insist, use different email addresses and connect them to different ID’s and online profiles.