You've probably seen the really big checks given to winners of monetary prizes. Are these checks valid?
Let's assume the oversized checks aren't valid. That means the people giving you the prize gives you a standard check after they take the picture.
The oversized checks are a prop. They are for PR purposes.
If you look at thr pictures the big checks are missing the name of a bank. They also don't include an account number. Your bank won't cash them or accept them for deposit.
Banks are no longer expected to accept checks that can not be scanned by their standard machines. This changed in the last few decades. See my other answer today.