A printer comprising: a printhead (22, 26) configured with a plurality of inkjets to eject material; a supply of thermal substrate configured to move thermal substrate to a position opposite the printhead to receive material ejected from the printhead; characterized by: an optical sensor configured to generate electrical signals corresponding to an optical density of a location on the thermal substrate; an actuator operatively connected to the optical sensor to move the optical sensor to a position opposite the thermal substrate onto which material has been ejected; and a controller operatively connected to the actuator, the optical sensor, and the printhead, the controller being configured to operate the printhead to eject a predetermined number of material drops from each inkjet onto the thermal substrate to enable the predetermined number of material drops to form a test dot for each inkjet on the thermal substrate, to operate the actuator to the optical sensor to a position opposite the thermal substrate, and to identify inoperative inkjets in the printhead with reference to the data received from the optical sensor that corresponds to optical densities of the thermal substrate at a plurality of locations on the thermal substrate. a printhead (22, 26) configured with a plurality of inkjets to eject material; a supply of thermal substrate configured to move thermal substrate to a position opposite the printhead to receive material ejected from the printhead; characterized by: an optical sensor configured to generate electrical signals corresponding to an optical density of a location on the thermal substrate; an actuator operatively connected to the optical sensor to move the optical sensor to a position opposite the thermal substrate onto which material has been ejected; and a controller operatively connected to the actuator, the optical sensor, and the printhead, the controller being configured to operate the printhead to eject a predetermined number of material drops from each inkjet onto the thermal substrate to enable the predetermined number of material drops to form a test dot for each inkjet on the thermal substrate, to operate the actuator to the optical sensor to a position opposite the thermal substrate, and to identify inoperative inkjets in the printhead with reference to the data received from the optical sensor that corresponds to optical densities of the thermal substrate at a plurality of locations on the thermal substrate. an optical sensor configured to generate electrical signals corresponding to an optical density of a location on the thermal substrate; an actuator operatively connected to the optical sensor to move the optical sensor to a position opposite the thermal substrate onto which material has been ejected; and a controller operatively connected to the actuator, the optical sensor, and the printhead, the controller being configured to operate the printhead to eject a predetermined number of material drops from each inkjet onto the thermal substrate to enable the predetermined number of material drops to form a test dot for each inkjet on the thermal substrate, to operate the actuator to the optical sensor to a position opposite the thermal substrate, and to identify inoperative inkjets in the printhead with reference to the data received from the optical sensor that corresponds to optical densities of the thermal substrate at a plurality of locations on the thermal substrate.