An apparatus monitors the motion of sheet, such as in a digital printer. An optical sensor is capable of recording an image in a two-dimensional array of pixels, and has acuity to recognize a terrain of a small area on a sheet that is substantially blank to a human eye. The optical sensor views a portion of a sheet moving in a process direction through a path. A detection system compares at least two recorded terrain images from the sheet, thereby directly measuring velocity and direction of the sheet.