Here is a list of websites which store avatars.
Gravatar - Globally recognised avatar-- propagates to most websites including Gitlab, Github, and the Matthew B. Gray page.
iCloud - Apple Stuff.
Google - Up to 2 days to propigate.
Linekdin - Curriculum Vitae.
Firefox - TODO Gravatar?
leetcode - TODO Gravatar?
element.io - TODO Gravatar?
See also Changing an Avatar.