Example embodiments relate to a method for applying a special mark, that is invisible to the naked eye, on a medium. That is, the example embodiments provide a method for generating and applying on a medium a digital spatial mark of X.times.Y dots in accordance with a resolution of d1x by d1y dots per surface unit, provided that the ratio d1x/d2x and or d1y/d2y is more than 1. The method further includes over-sampling the digital spatial mark in X based on a factor nx=d1x/d2x and in Y based on a factor ny=d1y/d2y; eroding the dots to be applied so as to leave one dot every nx dots in X and one dot every nx dots in Y; and applying the spatial mark on the support.