If anyone wants to cook a patch, that's ui.footer-items in https://phabricator.wikimedia.org/source/operations-puppet/browse/production/modules/phabricator/data/fixed_settings.yaml

I'd just add a disclaimer that all avatars, meme, tokens and uploaded screenshots are exempt from stated licenses.

Our footer is already a train wreck, but you could add a "credits" link to anywhere (wiki page maybe) that we can collect attribution for all non-PD but libre image content that is included in our UI additions. This is what a 'typical' site would do to comply with licensing guidelines for something like using https://commons.wikimedia.org/wiki/File:Goat_Noun_project_853142.svg as an icon. IANAL however, so take that advice with an appropriate helping of salt.

@Base: The icon is licensed cc-by-3.0.