Software is inherently required for digital photography, and opens up options for post-processing film as well.
Questions related to the tools used for digital image editing, processing, organization, and presentation should have this tag. These questions represent a large area of activity on this site, but aren't of interest to everyone — and are of particular interest to others. (We have a lot of "computer people" in the active user base.) Tagging such questions with software helps people find or ignore them.