I've been noticing the moving art between Dekalb Ave. and Canal Street but I have never gotten the chance record it. The way it works is that there are a bunch of pictures behind these little slits on the wall, so as the train is moving, you see the next picture and it almosts seems as if it's in motion. It's almost like the concept of a flip book. Here's a clearer video that I found.
I did some research and the one right after Dekalb Ave. and before Canal Street is named "Masstrasiscope" by Bill Brand.
Masstransiscope was an animated painting placed on the abandoned northbound platform of the Myrtle Avenue station, just prior to crossing the Manhattan Bridge. The animation was based on the zoetrope, essentially a series of single frames viewed through slits as the train moved past the station. The brief glimpses of the frames appeared to animate the artwork. The work has been in disrepair for many years but apparently some work is being done to it in September, 2006.
Apparently they use this form of subway art in other countries, such as Canada, as advertisements. The video below is a subway motion art in Russia. It must have taken a CRAP load of time to do that!