2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/3616We describe the Difference Image Analysis (DIA) algorithms and software used to analyze four years (1997-2000) of OGLE-II photometric monitoring of the Magellanic Clouds, the calibration, the photometric error analysis, and the search for variable stars. A preliminary analysis of photometric errors is based on the field LMC_SC2. A full catalog of about 70,000 variable stars will be presented in a separate publication.15 pages, 7 figures, revised version (accepted by Acta Astronomica)Astrophysicstext