-Image archive of ETH Zurich https://ba.e-pics.ethz.ch/main/galleryview (portraits of renowned scientists; photographs on the history of science and technology, landscape views)

-Image archive of the Metropolitan Museum of Art https://www.metmuseum.org/art/collection/ search?searchField=All&showOnly=openAccess&sortBy=relevance&pageSize=0 (art and exhibition objects, images of historical architecture)

-Image archive of the Smithsonian https://www.si.edu/search/collection-images?edan_q=&edan_fq=media_usage%3ACC0&oa=1 (images of art, culture, history, science and nature)

Image archive of the MKG https://sammlungonline.mkg-hamburg.de/de/ search?s=*&h=undefined&sort=scoreDesc (exhibition objects; architectural photography images with the addition "Public Domain" are freely available. This can be set in the filter options)

Image archive of the Deutsche Fotothek https://www.deutschefotothek.de/ (image archive of well-known photographers; paintings; maps; architectural drawings In the "Image description" under "Image rights" you can see whether the image may be used)

Stockphotos archives:

https://negativespace.co/ ;

http://pdpics.com 

https://pexels.com/ 

https://picography.co/