@editore

If the website in question is physically linking to your content and serving it from your web server, you can put a stop to hot-linking, though if they are copying & pasting content, saving and then uploading the images to their server, etc -- the best course of action would be to file a complaint with their web hosting provider (which I'd recommend doing anyway as putting a stop to hot-linking is most likely going to result in copying and pasting if they aren't already doing it).

You can do a quick lookup on the primary domain by using the website below. That'll at least give you an idea of who their web hosting provider is.

http://www.whoishostingthis.com/

If the site above doesn't give you a clear idea of who the provider is, then you can simply do a WhoIs on their domain to see if they web hosting providers DNS is listed for their nameservers.

From there, you can file a complaint and send an e-mail to abuse@nameofprovider.ext and CC a copy to support@nameofprovider.ext.

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That said, how you'd go about limiting content to your domain depends on your web server. Which web server are you using (i.e. Apache, NGINX, Caddy etc ... )?