[bcraven]

This site suggests it's just a remap:

The Venera panoramas are spherical projections. They can be remapped to perspective projections and overlayed (using Adobe Photoshop CS2) to produce views that give a better subjective impression of the Venusian surface

http://mentallandscape.com/C_CatalogVenus.htm

[ksymph]

That does seem to be what the page is implying at first glance; though the images clearly show features not visible in the raw photos, so it can't be the case. I'm guessing that paragraph is actually referring to the 'overhead' image [0] next to the one in question, since it mentions how the remapped perspective makes the uniform shadows apparent.

[0] http://mentallandscape.com/C_Venera13_Overview.jpg