1. A method for predicting a size of an image of an object in a field of view of a camera device, said camera device having an image plane including image elements, the method comprising determining at least one relevant spatial zone in the field of view, said relevant spatial zone corresponding to a possible position of the object based on assumptions on the relative position of the object; projecting the relevant spatial zone onto the image plane, thereby forming a projection; computing boundaries of the projection using camera parameters of the camera device to determine at least one relevant image zone; determining a directional beam for image elements in the relevant image zone, said directional beam including spatial points from the field of view; and determining, for each image element in the relevant image zone, at least one value for an expected size of the image of the object from assumptions on the size of the object and from a distance range based on the intersection of the directional beam associated with the image element and the relevant spatial zone.