We all push pixels one way or the other
Even in the most rigid environment for photographic-purism there is a demand for Photoshop. Whether it's used to color-correct images for press, create photo-illustrations for covers and interiors, or simply to design photo-intensive cover options.
I've always enjoyed working with hi-res files in order to see just what the final image is capable of achieving. It takes just as long to do the same things to a lo-res image, and if the design is approved in lo-res you take the risk of redoing the file in a slightly different mindset, especially if a bit of time passes between versions.
With the pieces shown here, Photoshop has been utilized to show something otherwise unavailable (or unobtainable), to create a mood, to enhance a specific visual cue, or to make art from photographic sources.
At Nat Geo, we were always careful to credit the sources of those combined images.