  We describe the methods and procedures developed to obtain a near-automatic
combination of WFPC2 images obtained as part of the WFPC2 Archival Pure
Parallels program. Several techniques have been developed or refined to ensure
proper alignment, registration, and combination of overlapping images that can
be obtained at different times and with different orientations. We quantify the
success rate and the accuracy of the registration of images of different types,
and we develop techniques suitable to equalize the sky background without
unduly affecting extended emission. About 600 combined images of the 1,500
eventually planned have already been publicly released through the STScI
Archive. The images released to date are especially suited to study star
formation in the Magellanic Clouds, the stellar population in the halo of
nearby galaxies, and the properties of star-forming galaxies at $ z \sim 3 $.
