Applications of Visual Cryptography - Visual Cryptography and Secret Image Sharing - page 337

FIGURE 12.13
Some parts of the encrypted image (C) is magnified for the observer (A),
while other parts are hidden. For example, d and j are in the focus while
b;c;e;f;h;i;k, and l are hidden.
FIGURE 12.14
Lenses are placed randomly on the slide (b). This can be done by spraying
a transparent liquid that becomes hard on the side. The area in the focus of
the lenses in the encrypted image (a) is colored in the color of the original
image at this region. The rest of (a) is filled such that colors in (a) are equally
distributed so that the original image can not be obtained from (a) alone but
only together with the slide (b).