Public Domain pictures, for backgrounds, establishing shots, etc.

[pacman000]

While exploring Project Gutenberg, I found this: https://www.gutenberg.org/cache/epub/70079/pg70079-images.html#Page_xi

It's an architecture book from the 50's, with over 100 pictures of buildings. Something tells me you'd still need to check them, to make sure they're really free, but it's a starting point.

If you know any other sources, post links here.