The above procedure has been built into IRAF code originally written by R. Hook and was tested both on simulated images (Caulet &Freudling 1993) and on actual WFPC images (Koo 1993). This is shown in Figs. 1 and 2. Additional WFPC observations with sub-pixel shifts between exposures are planned by R. Fosbury and will be used to further test this procedure.
