This paper describes an automated approach to maintain the alignment of modular direct marking print heads. An inline full width array sensor monitors the print head alignment and drop position within a print head by capturing and analyzing test patterns written to an intermediate drum. Unique steps are taken in illumination and calibration to ensure the structured drum media does not degrade the alignment measurement. The image is processed to identify the position of each mark. Interpolation and statistical averaging increase the accuracy beyond the resolution of the linear array. Both digital manipulation of the image and physical movement of the heads are used to maintain alignment.