Gravatar is a website which centralizes avatar managment. Various sites uses it, and not only RPGInsanity – for example, GitLab and WordPress uses it too.
You need to access gravatar website, create an account (it will require your e-mail), and then you can upload an avatar. And magically you’ll gain an avatar not only here, but in other sites which syncs with Gravatar too.
This is also great to save disk space on the server which could be better used with this reply 🙂
You can also just upload a basic Profile picture, and “crop-select” the part you want to use for your ‘avatar.’
I don’t use Gravatar by default on this site, and personally don’t like the Gravatar system, but unless the Gravatar “option” exists somewhere in all these pages, it won’t let me allow ‘avatar’ pictures, either. You can totally ignore Gravatar and it won’t hurt anything.