I missed this Planetary Society Weblog post a couple of weeks back (thanks to U Kuprasów for the tip). In her blog posts, Emily Lakdawalla sometimes features and discusses planetary images processed by people other than official mission staff (often by Emily herself). At the recent American Astronomical Society meeting, she gave a couple of presentations related to this (you can download them from her blog post).
Thanks to the internet, raw images from space missions are quickly available to anyone. Image processing software tools are widely available, and thanks to digital cameras, many people have skills with this type of software. This creates the opportunity to do things with the same imagery and data that the professionals use, to create interesting and beautiful images, and sometimes even scientifically useful images. She encourages "armchair scientists" to do this, and she encourages professional scientists and mission support people to provide them with the data to do it well, with benefits for all.
This is really a computer-based extension of observational astronomy, one of the few areas of modern science where amateurs can sometimes make real scientific contributions with their own observations. Thanks to the bigger telescopes and CCD cameras used by many amateurs, there are a lot more knowledgeable eyes on the skies (and screens) these days.