A code for the numerical analysis of images from a CCD camera, including correction of acquisition system defects, has been written and applied to the visualization of alpha-particle tracks in the solid state nuclear track detectors CR39 and LR 115. A standard mask having different diameter holes permitted the calibration of the imaging system. Comparison of manual scanning results with those given by the automatic system are presented for detectors exposed to alpha-particles of Am-241 source. As application, the system was used to measure specific activities of U-238 in the Moroccan phosphates and their phosphogypsums samples by contact autoradiography. (C) 2000 Elsevier Science B.V. All rights reserved.