Can I display other people's photos on my site?

Question

contextual advertising

Hello dear fellow web developers.
I want to create a website that will host photos found on the internet. The issue is copyright.
How correct and legal it will be to post other people's photos not for download , but for demonstration . Photos will be placed in large volumes - something like a landmark of cities. There will also be an opportunity for authors to contact the administration and claim their rights. The volume will be such that finding the author for each photo and asking for permission is not realistic either in terms of time or strength, and the authors cannot be found with just one photo from the Internet. How correct will it be to place contextual advertising next to a photo of someone else's author, is this allowed in AdSense or YAN?
Thank you.

Answer 1

Well, something like this https://geektimes.ru/post/243463/

Answer 2

It is purely technically impossible to take photos just "for demonstration". The file is still downloaded to the user's computer.

Answer 3

Illegal in general.
In fact, few people complain. And if you give a link to the source, they will also be satisfied.
There is also such a thing as a CC / PD (Creative Common / Public Domain) license.
If the original photo is under this license, then everything is easy and simple.