I used to work a few years ago with a smart guy, a statistician. He used to visit Las Vegas & Atlantic City casinos frequently, and he was a card counter. He made some money but not enough to quit his day job by any means. It got harder and harder for him because the casinos captured his face through facial recognition software and he was banned in many of casinos. I don’t think anyone could become a millionaire through card counting in this electronic surveillance age.
I had a friend who did the same thing. He, too, was banned from casinos. That was in the ‘70s and ‘80s, probably before high-tech facial recognition via biometrics. Good old-fashioned photographs, I believe.