A user interface for use with a networked printer and computer system includes a sheet of media printed with both visible and invisible ink, such that the visible ink indicates information for a user and the invisible ink depicts coded data. The invisible ink is detectable with a sensor that is configured to generate a signal carrying said coded data that is received by a computer system connected to the printer, in use. The coded data is represented by an array of printed tags which cover at least a portion of the sheet of media. The tags have at least one common target structure and each tag has at least one data area with coded data representing at least one set of bits that define a characteristic of the sheet.