How to serve non-static images (from server to browser)?

I understand how to serve static images by referencing the public or assets directory in HTML img or CSS url. However, I'm not sure how to store, serve and handle private images.

Let's say we have a client-server communication like in SPA's.

First, are these private images stored in a different, private directory on the server (and their path locations in a database) or stored as base64 in a database directly?

How do you send the private image from the server after checking for credentials? Base64?