A machine moves shoe strobels to a camera or scanner where images of the strobels are captured. Using the images, a computing device instructs a printer how to mark guidelines within a threshold distance of each other on the strobels that signify strobel sewing lines for different shoes models and shoe sizes. Cross-sectional lines may also be printed on the strobels to aid in error-checking guideline marking. Unmarked strobels are stacked in a loading compartment, sometimes in pairs—e.g., right and left shoe strobels. The unmarked strobels are transferred to a conveyor that brings the strobels to the camera or scanner and the printer. After guidelines and/or cross-sectional lines are added to the strobels, the marked strobels are stacked in a compartments housing other marked strobels.