Yes, i am aware that taking pictures of the screen is always possible. I was looking for a best effort solution, because blocking screenshots and sharing would definitely do most of the work. I don't know why people immediately jump to DRM. It's just an image viewing app that I'm looking for.
The social issue is, that my SIL already asked that none of her kids be posted to social media, but my BIL ignored that.
But since there doesn't seem to be anything like that, I guess I'll have to tell them that if they ignore it, they're will be no more pictures
So steam, basically? Less likely that they'll be shutting down anytime soon, but still.
Edit: people downvoting don't seem to understand how steam works