Well, non-copyrighted Images can be hard to find if you don’t know where to look. I found a couple of articles that list a good amount of non-copyrighted images for your story. I have used some of the websites on the list when I do request for episode edits, looking for backgrounds, and good backgrounds for pfp pics. I can definitely vouch for both pixabay and pexels for sure. Check out the lists below to see if you can find anything that will look good as the cover image for your story, backgrounds, and even more.
https://www.muo.com/tag/top-5-websites-for-free-stock-photographs/