According to one aspect of the invention, a printed security device for
a document comprises an intaglio printed latent image which has been printed onto
a substrate using a highly reflective ink, wherein the intaglio printed latent
image is visible when viewed within a first angle range extending from near-vertical
to the plane of the latent image towards the image and also within a second angle
range closer to the plane of the image, and is not visible when viewed within an
angle range between the first and second angle ranges. A change in viewing angle
from one angle range to an adjacent angle range results in a visible latent image
becoming invisible or vice versa (creating a flip-flop image visibility effect).
According to another aspect of the invention a non-intaglio printed second image
is added, preferably between the substrate and the intaglio printed latent image,
wherein the second image is visible when viewed within an angle range between the
first and second angle ranges of visibility of the intaglio printed latent image
and is not visible when viewed at other angles. The flip-flop image visibility
effect is thereby enhanced such that distinct images (viz. the intaglio latent
image and non-intaglio image) are viewed as the viewing angle of the security device
moves from near-vertical to near-horizontal angles.
