...but I was able to put together this painting in pretty short order (about a half hour?).
The software is called ArtRage, a free download from ambientdesign.com, a company that writes plugins for photoshop. I did this one on a Tablet PC, using an existing photo as a Tracing Paper, with Choose Colors Automatically turned on. It was amazing to watch the full painting take shape. This is extremely easy to use, and the results are pretty impressive.