How to correctly store backend images for a React - Node web app with many users

Question

I have a web app hosted on DigitalOcean that is based on React and Node technologies. The app is supposed to be used by many users and they will generate a plenty of average quality images using the backend R scripts. So, the images can not be directly stored on the front end.

I have not yet implemented user registration and currently the app is just writing complexly named .png images on disk for all of the users. I think that it is a wrong way to go and I am wondering how I should approach the problem. The app is running Neo4j database. If you could provide a structured answer on what should be done (for user registration, then for image storage) with the right node packages for it that would be awesome.

I think I should use DigitalOcean s' S3 storage for it, but it is not clear what should be step-by-step process.