US Patent 9536162 Method for detecting an invisible mark on a card

The present invention relates to a method for detecting a mark that is invisible in the visible light region. Here, the invisible mark is displayed on a card using a characteristic according to which the color of light is changed by means of a refractive index difference according to media in the visible light region. According to the method for detecting the invisible mark, it may be quickly determined whether the card is a counterfeit card in an investigation. In addition, since it is unnecessary to repeatedly inspect the card to be checked using various wavelengths, the time required for determining whether the card is a counterfeit card may be reduced.