Marked Cards Detection Methods
In recent years, cheaters have devised ways to mark decks of playing cards so that they can discern a card’s rank and suit on the back. This enables them to gain an advantage over the casino (e.g. blackjack) or other players (e.g. poker). The mark can take the form of invisible chemicals viewable with special lenses, bending or crimping, solvents that smear existing inks, tintwork and shading, and various other visual demarcations and anomalies.
These methods can be detected by manual inspection or electronic scanning. A polarized light source can detect some forms of tampering, while a non-polarized light can reveal scratches and pinholes that are invisible to the naked eye. A scanner that combines color and monochrome imaging can also detect certain marks by their shadow or reflectance.
A more sophisticated way to mark a deck of cards is to use luminous marking. These marks can be seen by a person wearing a pair of specialized contact lenses or glasses that can display a purplish light on the cards. Other types of marks can be spotted by riffling the cards carefully while looking for patterns or variations in color or shade.
Recently, Blazevic has developed a device called the Spectrum Vision SV-1 that is capable of detecting some types of markable cards. He showed the device at a number of gaming events including the Global Gaming Expo, ICE Totally Gaming and the World Game Protection Conference. He inserted a sample card with daub in the corner and then cycled the Spectrum Vision SV-1 through different light wave frequencies to show how the daub was visible under each condition.