Over at the KTOG (Kel-Tec Owner’s Group) Tim Tackett posted up a how-to-guide to painting digital camouflage on guns.
He basically uses a natural sea sponge and dabs on the paint. It is not quite digital, but the results are not too bad. There are some specific tips of things to avoid due to the nature of the paint he uses.
He uses Aervoe Military spray paint. You can find it here.
It comes in a decent palate of colors.