The https://www.britishmuseum.org domain is where the recently updated collection of CC-licensed images are available for public reuse, refer to https://www.smithsonianmag.com/smart-news/british-museum-makes-19-million-images-free-download-180974799
Though these are by default cc-by-nc, many are simple scans and public domain by age. Refining the collection query by age and object type can return only public domain images with a high degree of accuracy.