1. A method of classifying objects using volumetric multi-energy CT images, wherein a CT image, a Z (atomic number) image and a label image are provided, the method comprising: a. Acquiring CT density data for a region of interest (ROI) for detection of a potential threat object within the data using dual energy x-rays, wherein the region includes at least a portion of the inside of a container; b. Dividing the potential threat object into different geometrical portions using the label image on a slice by slice basis; c. Computing the local distribution features for each portion of the potential threat object on a slice by slice basis for both volumetric CT images and volumetric atomic number images, wherein computing the local distribution features includes computing local density distribution features of the volumetric CT images and computing local Z (atomic number) distribution features of the volumetric atomic number images; and d. Classifying the potential threat object as a threat or a non-threat using the local distribution features of both the volumetric CT images and volumetric atomic number images.