There is a debate in some circles over the use of post-processing software like Photoshop when producing a photographic image. There are people who call themselves 'purists' who feel that somehow an image processed with Photoshop isn't a legitimate photograph. While I admire the purist idea, I think in most cases the notion of a 'pure' image is a false one. In fact, short of using a pinhole camera, almost every image (film or digital) is 'processed' in some manner simply by the selection of camera, lens, film, ISO, filtration, development chemicals (if film) or the JPEG settings on a DSLR. All these factors contribute to the final image and affect the purity in one way or another.
When I shot film I was in the anti-Photoshop camp. Photoshop acquired a reputation as a tool to use to falsify an image. However, after some more reflection, I realized this was a bad rap. Photographers over the years have found ways to manipulate their images, whether to help them reach the artists full visualization, or to create something fake. I remember reading articles in photography magazines about how to make multiple exposures, perform various darkroom tricks, etc. to enhance or create an image. Using Photoshop (or similar tool) on a digital image is no different.
There are some statements by Ansel Adams in his book The Print which I find particularly pertinent:
"Much effort and control usually go into the making of the negative, not for the negative's own sake, but in order to have the best possible 'raw material' for the final printing."
"In printing, we accept the negative as a starting point [emphasis mine] that determines much, but not all, of the character of the final image. Just as different photographers can interpret one subject in numerous ways, depending on personal vision, so might they each make varying prints from identical negatives."
It is my belief that the use of Photoshop on a digital image is akin to the darkroom development and printing process used to create negatives and prints from film. Chemical darkroom work is probably technically more challenging, but the output is no more or less pure than an image produced from the digital darkroom.