1. A printer comprising: a print engine having a plurality of nozzles to apply print data to a medium; a print verification system (PVS) to read the print data applied to the medium; and a control unit to receive image data from the PVS and analyze the image data to locate artifacts on the medium caused by defective nozzles and to classify a first artifact associated with a first optical density (OD) signature as a first defect type and a second artifact associated with a second OD signature as a second defect type, wherein the first OD signature includes an undershoot characteristic and the second OD signature includes an undershoot characteristic.