Today I set up Folleon's page on LinkedIn so I had to add a nice-ish background image that looks not too bad. That leads me to...
The recommendation of the day: PxHere (https://pxhere.com), pictures "Free of copyrights under CC0. Do whatever you want."
They explain (https://pxhere.com/en/license) the license details (https://creativecommons.org/publicdomain/zero/1.0/) as follows:
It's hard to understand complex licenses that is why all photos on PxHere are licensed under the Creative Commons Zero (CC0) license. This means the pictures are completely free to be used for any legal purpose.
The pictures are free for personal and even for commercial use. You can modify, copy and distribute the photos. All without asking for permission or setting a link to the source. So, attribution is not required. The only restriction is that identifiable people may not appear in a bad light or in a way that they may find offensive, unless they give their consent.
And the pictures are good! If you want to build a hipster-like site where you have these generic shots from the top with a mac, a cup of coffee, and probably something to write, just (https://pxhere.com/en/photo/1338927) take (https://pxhere.com/en/photo/831487) one (https://pxhere.com/en/photo/1087236) or (https://pxhere.com/en/photo/1066963) two (https://pxhere.com/en/photo/1188058).
You have to sign in to download the images. But that's IMO fair enough.