The Waldo zk proof isn't a good example. You can easily fake knowing where Waldo is by gluing a Waldo to the board you use to hide the book. That way you can even proof you know a solution for a picture that doesn't even have Waldo in it.

It's a perfectly fine example! It doesn't have to be academically rigorous, it just has to demonstrate the basic idea of proving a thing without exposing the thing. Yes, obviously it's not actually a formal ZKP, but analogies are imperfect.

This can easily be remedied by having the verifier ensure the prover is in an empty room, equipped with only cardboard and scissors.