I wanted to upload a nice picture to my profile, but apparently I cannot. What is the purpose of that "gravatar". Why wouldn't I be able to have a picture displayed on all my accounts, just like my profile is?
Gravatar is a third party service for global avatars:
Your Gravatar is an image that follows you from site to site appearing beside your name when you do things like comment or post on a blog. Avatars help identify your posts on blogs and web forums, so why not on any site?
The benefits are outlined in this blog post:
I’ve used Gravatar for a while myself, and over time I’ve really grown to appreciate their approach:
They’re global. They work across every website that supports gravatars. Sign up once, benefit everywhere.
They’re easy. It’s totally straightforward; you simply build a URL that contains a hash of your email address (or IP address, if you didn’t provide email) add a few mostly optional preferences in the querystring, and that’s it.
They’re safe. The Gravatar service vets the images so nothing, er.. disturbing.. shows up in your browser. You can specify whether you want a maximum rating of G, PG, R, or X for gravatars displayed on your site. We’re going with PG; I hope you guys and gals can handle that kind of intensity.
It does one thing. Gravatar isn’t about social networking, mp3s, news, or any mashups thereof. It’s trying to solve one tiny problem on the web with laser-like focus: providing a web-friendly Globally Recognized Avatar for you across all the websites you visit. It’s almost a single serving website, and I say that with the utmost respect. So many websites fail because they try to do everything and be everything.
So, you can of course upload a picture and have it displayed on all your Stack Exchange accounts, the only thing you need to do is sign up for Gravatar and upload the picture there, taking care to use the same email you use for your Stack Exchange account.