@montoneserg – Not sure where you got the impression we can lock down directly accessed media from your server. To be clear that process does not ever even touch WordPress. Requesting a file via direct access url connects directly to the server and retrieves the file. WordPress is bypassed and as such a WP plugin could never protect files in that sense.
In all honesty you can’t protect them in any real sense if they need to be inserted onto pages somewhere. If you password protected the folder the images were on (at the server level) users would be required to know that password (different from their user login). Otherwise you simply need to lock down the pages those images would be viewed on which prevents the URLs from ever being leaked without permission.
IE. if I can view them on your site I can grab the link from the html and access it directly just like the browser did to load it for your site.
If I misunderstood let me know.