There is provided a method for assigning an attribute to an unknown object overlapping with a predetermined background object. The unknown object is scanned overlapping with the background object within an x-ray scanning device to obtain a plurality of dual-energy attenuation images having attenuation information representing the background object and an overlap region wherein the background object and the unknown object overlap. The dual-energy attenuation images are decomposed into reference material equivalent path length images. The reference material equivalent path lengths representing the background object in the overlap region are determined and eliminated from the overlap region to provide reference material equivalent path length images having first and second reference material equivalent path lengths through only the unknown object.