An image is recorded of the edge of a moving object, in particular a sheet, in a machine processing printing material. The illumination is carried out with an illuminating device, and an image is recorded of at least one part of the edge with an image recording device. The use of the illuminating device and/or the image recording device is substantially synchronous with the movement of the object and substantially parallel to the direction of movement of the object. A preferred illuminating device has a row or array of light sources which in each case are switched on and off synchronously with the movement of the object. The constant shadow or shadow strip produced by the illumination moves with the object and ensures adequate contrast between the brightly illuminated object and the dark background, so that the object can be segmented reliably, at least in the region of the edge, and its position, orientation and movement can be determined.