They are perforated, to resemble the punched paper tape Tutte was so familiar with, and when viewed from one particular direction reveal an image of Tutte's head and shoulders.

BBC: Suffolk

Optical correlators, meanwhile, work by encoding images on to a beam of light and, using a special lens, transforming them into their Fourier components building-blocks that encode the thickness and direction of lines in the image, but not their position.

ECONOMIST: Optical recognition

But traditional holograms appear distorted if the viewer is not looking at the image from the right direction.

FORBES: Magazine Article

Image via CrunchBase Predicting the direction of financial markets is an enticing proposition that has attracted the interest of scores of experts, who claim to have the magic formula.

FORBES: Zipcar