Recently most browsers have gotten stricter when handling requests from inside Javascript that target domains different from the script's origin (the page executing the script).
This repository contains slides for a quick talk titled "CORS primer" as well as an example how to configure CORS inside a SpringBoot backend.
Most images provided by Martin Vorel licensed under CC0 - Public Domain license & Royalty free. He has a whole webpage full of cool photos all under public domain licenses.
Also thanks to Pexels. They provide a huge selection of images under the "Pexels License" (completely free to use).
Same goes for Pixabay. Their license is also pretty much as free as it gets.