They say that the North Korean “super hundreds” are actually more precisely engraved than actual U.S. currency.
I was working in Chico, Ca. a while back and the GM at the store said there were counterfeit $100 bills circulating. The paper felt genuine, the ink was good, the thin embedded strip was good. The only way you could ID it was the green seal on the lower right corner, if you looked at it carefully you could see that the ink was flat and not raised.
He was there edumacating the employees.