One of my favorite websites to go on for visual inspiration has to be Wikimedia Commons, which you might stumble across when clicking on an image in Wikipedia 
occasionally. Like Wikipedia, everything is freely licensed, not trying to sell you stuff, and must serve an educational purpose. You can really learn a lot 
about the world just by hitting the random file button and exploring the categories at the bottom of an image's page; unlike Wikipedia, the random button is 
actually interesting. Most of the photos have a share-alike license, meaning you probably will have a hard time using them in commercial projects directly, but 
Commons's biggest strength is probably its historical collections, which are mostly scanned very high-res from museums around the world. I'll take this article 
to highlight some of my favorite collections from my time on the site.


Public Domain


Old biological illustrations of mostly fish, plants, and birds.

h	URL:https://commons.wikimedia.org/wiki/Category:Kawahara_Collection_at_Naturalis_Biodiversity_Center


Hundreds of thousands of old maps from the Library of Congress; note you can search by category by adding incategory:"category name" to your search.

https://commons.wikimedia.org/wiki/Category:Maps_in_the_Library_of_Congress


Old book covers from the Smithsonian Design Museum. Pretty unique textures.

https://commons.wikimedia.org/wiki/Category:Albums_in_the_Cooper%E2%80%93Hewitt,_Smithsonian_Design_Museum

Their interior design collection is also pretty neat.

https://commons.wikimedia.org/wiki/Category:Interior_design_drawings_in_the_Cooper%E2%80%93Hewitt,_Smithsonian_Design_Museum


Illustrations from some type of fashion magazine or something? White background so these might have a use somewhere.

https://commons.wikimedia.org/wiki/Category:Alexandre_Lacauchie


More plant illustrations.

https://commons.wikimedia.org/wiki/Category:Flora_by_H._Witte_(pngs)


Graphs and illustrations from a late 1800s science magazine; really cool. Flip through the volumes with the numbers on the top of the page.

https://commons.wikimedia.org/wiki/Category:Popular_Science_Monthly_illustrations/Volume_57


Prints from a Dutch museum. Very interesting compositions.

https://commons.wikimedia.org/w/index.php?title=Category:Willet-Holthuysen_collection


Thousands of modern photos of anything to do with farming from an agency of the USDA, lots of high-res landscapes and fruit. 

https://commons.wikimedia.org/wiki/Category:Natural_Resources_Conservation_Service


Non-Public Domain


Railway line in Russia, highlight on the nighttime photos

https://commons.wikimedia.org/wiki/Category:Kerzhenets_peat_narrow_gauge_railway


A bunch of old objects.

https://commons.wikimedia.org/wiki/Category:Objects_in_Sec%C3%A0_i_Muntanya_exhibition,_Museu_Valenci%C3%A0_d%27Etnologia