If you save down one of the images and up the gamma a little, you can see a tremendous amount of detail. Far more than could practically be done by hand, and afaict, more than PyEphem has in its catalogue of "bright stars".
I suspect he used something like Stellarium and then ran the images though some filters.
http://forums.xkcd.com/viewtopic.php?f=7&t=101043&p=3395021#...
http://rhodesmill.org/pyephem/