All files inside a public/ directory in the root of the project are considered static and will be copied over to the build/ directory.
It's the perfect place to add fonts, images, videos and any other file that should be public.
You should also add any .css or .js files that doesn't have to be pre-processed.
Use the sweet-potato-masher to optimize yor images. Simply run:
npx @wethegit/sweet-potato-masher