Where you can get high-resolution photographic images.

I'll share some of the sites I use. For your information, you must check the copyright when searching for free images on Google. I've summarized the copyrights a little copyrights below.

https://www.pexels.com/

https://unsplash.com/

https://pixabay.com/ko/

The Creative Commons Zero is a mark created to display the public domain.

In this way, it means that it is a content that can be used, shared, modified, and redistributed by anyone whose copyright has expired. To put it in a bit of a difficult way...

 - When the author gives up the copyright by expressing his or her intention
 - If the copyright protection period has expired
 - Where laws and regulations stipulate the extinction of copyright for a particular work;

You could say that. See Wiki for more information. Creative Commons license / Public domain