Is there a law on casino money won?

Yes, lots of 'em. Each state has their own sets of laws and federally, you are supposed to claim your winnings, but that's pretty much on the honor system. When you claim your winnings on your federal tax, don't forget to subtract your losses. You can easily obtain a win/loss report from the casinos you frequent if you call them, or stop by their customer service or players club booth. If you don't have a players' card at that casino, though, getting a win/loss report will probably be difficult or impossible. Casinos are not required to send the win/loss reports to the feds, so don't worry if you feel the amount you have won is too insignificant to claim. The IRS won't come and take you away or anything. I would, however, strongly advise you to claim any winnings in excess of $10,000. If you made $10,0000 all in one day, you're going to be on the radar anyways, because, just like banks, casinos are required by federal law to fill out a CTR (currency transaction report) for cash transactions over $10,000. These are not sent to the IRS, but to homeland security, to identify possible cases of money laundering. But if one government agency has this information, how hard would it be for the IRS to get wind of it?
Beyond the federal, the only state I can answer for is Indiana. If you win a jackpot of $1200 or more in the state of Indiana, 3.4% state tax will automatically be taken out. You can get this back if you are not an Indiana resident, although I hear that can be quite a hassle. If you win a drawing, you may be required to pay state taxes also. Just remember, though, if you don't have your current drivers license, state ID or passport with you when you win a drawing or jackpot, you will not be able to claim your prize until you can produce one of those valid documents.