Masterlist of Public Domain Visual Stuff

Hermetically Open Project - occult texts

Open Access at the MET - art history

British Library - miscellaneous

USGS Bee Inventory and Monitoring Lab - bees and related macro photography

Game-Icons.net - black and white icons

Smithsonian Open Access - miscellaneous

Rawpixel - miscellaneous

Public Domain Review - miscellaneous

Alan Mays - miscellaneous

Elusive Muse - herbs; codex seraphinianus

Rijksstudio - art history

Unsplash - miscellaneous

Library of Congress World Digital Library - miscellaneous

Getty Museum Collection - historical art