This diagram shows sunlight entering from behind while the artwork is sandwiched between two polarizing filters. The front filter is slowly rotated.
The cover filter fits snugly onto the art frame. The artwork changes color by manually rotating the cover filter ninety degrees.
These old articles describe the origin of polarizing filter art first appearing with filter innovations by Polaroid. I find the earlier articles most entertaining with their accounts of the Kinetichrome and, of course, the Abstractoscope.
The below collection of art is photographed through the hand viewer.