A printer for printing on an outer layer of a print medium on a print medium roll. The printer includes a base and a cover, which are pivotally coupled in a "clamshell" configuration for movement between a closed position in which the printhead is located in a printing position proximate the path of the media and an open position that is spaced from the printing position. The printer may use thermal or inkjet printing. The printer is used without a mechanical paper drive mechanism. The printer monitors movement of an outer wrap of the print medium as the print medium roll rotates in response to a user pulling print medium from the print medium roll. In one embodiment, the printer detects movement of the print medium with a metering roller and an optical rotation sensor. In another embodiment, the printer monitors movement of the print medium by detecting movement of index marks on the print medium. From the monitored movement of the print medium, the printer identifies a portion of the print medium aligned to the printhead and selects image portions to print in the identified portion. The printer then activates the printhead to print the selected image portions in the corresponding identified portion. A bias spring, together with movable mounting of the printhead, allows the printhead to remain engaged with the print medium as the radius of the print medium roll decreases as the print medium is dispensed.