Marked cards invisible ink, as the name implies that it is one kind of ink marking backside on playing cards and we cannot see through by naked eyes. But there have methods which can detect invisible ink marks. For example, infrared/UV contact lenses and luminous ink sunglasses can read its marks which are luminous and clear. Poker analzyer with poker cheating camera can scan its secret marks for telling you poker odds results. IR camera can read infrared invisible ink marked cards, etc. www.cheatpoker.com