We use a third party service called Gravatar to create and use profile images. On Gravatar you can upload and create a rudimentary profile and then when you participate in any Gravatar-enabled site, your Gravatar image will automatically follow you there.
Gravatar is a free service for site owners, developers, and users. It is automatically included in every WordPress.com account and is run and supported by Automattic.
If you need to check your Gravatar to see how it will appear, they've set up a page where you can check the Gravatar for your email. Enter your email address and click check.
More about Gravatar here.