If you don't want anyone to pass off your photos as their own, steal them, or mess around with them, then you shouldn't post them online. This problem is as old as the internet itself. Let's be honest—watermarks don't stop anyone these days. Any AI can remove them. Or just generate images using your face and body. And if a watermark is important to you, just add one yourself. *shrug*
And yes, my photos have been stolen before, too.