Just had a look at it, and though I like the idea, I'm not sure how to implement it.
Because actually, there don't seem to be any standard way to get an avatar in Jenkins.
Do you have avatars in your Jenkins installations? If so, could you please show some screenshots + ideally the additional plugins you installed to do that?
Because the solution might also be to put that addition in that plugin since I made the buildtriggerbadge extensible some months ago through an extension point.
Thanks for the feedback!