They are lovely, aren’t they? It’s a cruel trick that they are on the wall outside the shop, because it did make me think that they’d be for sale!
They use a lenticular system, where a grid of plastic lines is placed over a sheet which has been printed in corresponding sets of narrow bands, the prismatic quality of the plastic letting each eye see only one of the sets at a time, and as you move either it or yourself, the image changes slightly. It allows for “3D” pictures, or for an “action” to take place.
The new musical “The Woman in White” has some of their posters done in such a way that they appear to show an empty landscape at first, then as you go by a ghost appears to fade in - it’s very effective.
Hats off to the person who came up with that display at the museum - it’s a very novel and appropriate use of an effect. | 
