I expected at least a dozen people to leap in here with the difinitive answer.
But they didn't.
So I will put my litttle knowledge to some use.
In the LWB of my US Games Thoth, it says that the original paintings measure 10 1/2" by 16 1/2"
There is no mention of if this includes the borders or not.
So, not very big really. But bigger than the cards.
Hope this helps