Interferometric techniques described in this paper permit real-time optical image subtraction of two input photograph transparencies without the necessity of intermediate processing steps (e.g., holograms or contact-print transparencies). These interferometric techniques allow the use of a white-light source as well as an extended light source, small input-collimator optics, and optical components with minimal requirements on wavefront quality. Experimental results with NASA LANDSAT (formerly ERTS) photographs are presented.