You can actually do some of this at home if you have a blacklight, a drawing table, and some fluorecent markers or paint (http://www.blacklight.com/items/BLWPNT46
I used to know someone who used to do this all the time, all you have to do is make a drawing with regular paint or markers, then go over it with the fluorecent kind. Depending on the kind of markers and/or paint you use it will be visible or unvisible in normal light. But either way, you can get a totally different drawing under a blacklight. It's pretty cool
Offcourse the work on that site surpasses all of that and is done very professionally, it looks really great.