lenticular lens

A lenticular lens is an array of magnifying lenses, designed so that

example of lenticular lens art

when viewed from slightly different angles, different images are magnified. The most common example is the lenses used in lenticular printing, where the technology is used to give an illusion of depth, or to make images that appear to change or move as the image is viewed from different angles.

http://www.youtube.com/watch?v=HnSSwia4Fno
https://www.youtube.com/watch?v=gOZI1tlNo0Y

The vision of a house fly has same principle.