Use Your Picture WordPress User how? It is simple I did not knew ever before I found the site http://en.gravatar.com/
I was dreaming to use my own image as a WordPress gravatar. Now I know how to do that? This will work for both http://wordpress.org/ and http://wordpress.com/ . The process is so simple just you need to register with your email address you used for WordPress user or want to use. All done after registration upload your photo.
One important message for you that the email you registered for the gravatar site and it will work (same image) for your all WordPress website user. The image will show into wordpress user as a gravatar.