1. A method for analysis of a digital image comprising an array of pixels and including a plurality of objects, which method comprises using a computer or processor to perform the successive steps of: (a) identifying locations within the image of those of said objects which have specified intensity and size characteristics; (b) defining respective local regions of interest within the image around those of said objects which have said specified intensity and size characteristics; (c) deriving from data within said respective local regions one or more respective closed contours comprising points of equal intensities; and (d) estimating the curvature of at least one of said respective closed contours within said respective local regions and producing at least a measure of any concavity thereof.