1. A method of computerized detection of clustered microcalcifications in a digital mammogram derived from an original radiographic image, comprising: producing a multi-pixel difference image of said digital mammogram to remove low-frequency structured anatomic background; performing a global gray-level thresholding of said difference image to produce a global thresholded image, including producing a histogram of the difference image, setting a global threshold based on a pre-selected percentage of pixels at the high end of the histogram, retaining unchanged in said difference image those pixels having a value above said global threshold, and setting to a predetermined constant the values of those pixels in the difference image which have a value below said global threshold; performing area filtering by means of morphological erosion on the image data resulting after global thresholding thereby to produce an area filtered image in which small signals are selectively removed; and processing said area filtered image in which small signals are selectively removed to identify microcalcifications; wherein said step of performing area filtering comprises: defining plural structuring elements each having a size of at least two pixels, sequentially defining each pixel in the image after global thresholding as an operating pixel and sequentially overlaying each operating pixel with each structuring element; determining, for each operating pixel sequentially overlaid by each structuring element, the minimum pixel value of the pixels overlaid by each structuring element in relation to the same operating pixel; determining the maximum of the minimum pixel values determined in relation to the same operating pixel; and setting the value of each pixel in the output area-filtered image corresponding to the position of the operating pixel in the global thresholded image to the respective maximum of said minimum values determined in the preceding step.