bwin wikipedia

Important callout: Certain gambling winnings are exempt from US tax, including blackjack, craps, baccarat, roulette, or big six wheel. Non-US residents who win the national lottery will be subject to a 30%-38.8% withholding rate if winnings exceedR$599.99.

There's no gray area in the U.S. tax code, though. It says that you must pay taxes on money that you earn if you are a citizen of the country. That includes money earned through gambling  this goes beyond mere poker games  and it counts money you earn overseas.