A communication card system (101) comprises a second communication card (2a), a second information processing system (3a), and a user terminal device (51) . The second information processing system (3a) synthesizes hidden image data to be communicated in main image data for display and provides such composite image data. An image display/recognition system (5) includes the user terminal device (51a) which displays main image data and displays hidden image data in a invisible manner. The second communication card (2a) having an optical medium (23a) of optically transmissive characteristic is used for visually recognizing hidden image formed by hidden image data displayed on the user terminal device (51a).