1. An image processing apparatus for computing a quantitative imaging biomarker (QIB) of disease severity from variations in texture-based features in a tomographic image, the apparatus comprising: a first module for preprocessing by normalizing the intensities in the tomographic image; a second module for identifying at least one organ of interest in the tomographic image; a third module for identifying and selecting a plurality of target region of interest (ROIs) and reference ROIs representative respectively of abnormal and normal pathology in the organ(s) of interest; a fourth module for extracting a plurality of texture-based feature signatures from the target ROIs and the reference ROIs, wherein the feature signatures are generated from distributions of statistical attributes extracted from each ROI; a fifth module for computing the distance between the target ROI signatures and the reference ROI signatures, wherein the QIB quantitative imaging biomarker is a function of the distance between the target ROI signatures and the reference ROI signatures wherein the distance is computed using the Earth Movers Distance or the Divergence of Kullback-Leibler.