No that's not the thing about it. The thing is you put the cardboard over the book then show it to the other person.

The other person won't know where Waldo is, because the cardboard is much bigger than the book, so Waldo could be anywhere on the page.

That’s not what OP was referring to. OP was saying the hole still reveals a little information (Waldo’s Size/shape/posture) to the opponent.

The cardboard would need to be at least twice the dimensions. Otherwise it's possible that the book could be seen past the edges.

Twist the example in the paper a bit, to create a shape of Waldo's face and show only Waldo's face.

Do note, the information we are concealing is where Waldo is, and not how he looks.

Maybe you can show only Waldo's face?

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.