Is there a way I can upload a picture to your service instead of Imgur? Or possibly use a gravatar link or from a webpage like Google?
We use imgur for image hosting, so if you want to use the direct upload feature, that's really your only option.
Gravatar is still supported, but take note that this exposes a MD5 hash of the email you've given to Gravatar:
To get there, go to your profile by clicking your avatar on the top center of the screen, then navigate to the "Edit Profile & Settings" tab:
Worth mentioning that you can link to any external image in pretty much any place that markdown or HTML is rendered, but the actual profile picture itself is tied to one of the three buckets we offer there.
It's been a long time since I signed up using a Google account, but I believe we now capture the associated avatar during signup, and ask you if you want to use it (or offer the custom upload, identicon, etc).