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.
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 firstname.lastname@example.org and CC a copy to email@example.com.
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 … )?