A handheld display device for imaging a printed substrate and revealing hidden content associated with the printed substrate. The device comprises: an optical sensor for imaging an area of the printed substrate and for generating image data; a processor for determining interaction data using the image data, the interaction data identifying a substrate identity; a transceiver for retrieval of display data corresponding to the printed substrate, the display data comprising first data corresponding to the printed content and second data corresponding to the hidden content; and a touch-sensitive display screen for displaying display information based on the display data. The display information includes first content corresponding to the printed content and second content corresponding to the hidden content, thereby revealing the hidden content on the screen.