An optical variable device or optically variable device (OVD) is an

iridescent Iridescence (also known as goniochromism) is the phenomenon of certain surfaces that appear to gradually change color as the angle of view or the angle of illumination changes. Examples of iridescence include soap bubbles, feathers, butterfl ...

or non-iridescent security feature that exhibits different information, such as movement or colour changes, depending on the viewing and/or lighting conditions."More about Optically Variable Devices (OVDs)" ''Product Authentication & Security Directory''
/ref> The particular changes of appearance when rotating and tilting are reversible, predictable and reproducible. OVDs cannot be photocopied or scanned, nor can they be accurately replicated or reproduced. OVDs are often used as security devices and anti-

counterfeiting To counterfeit means to imitate something authentic, with the intent to steal, destroy, or replace the original, for use in illegal transactions, or otherwise to deceive individuals into believing that the fake is of equal or greater value tha ...

measures on banknotes, government-issued identification documents, or credit cards. OVDs can be created through a combination of

printing Printing is a process for mass reproducing text and images using a master form or template. The earliest non-paper products involving printing include cylinder seals and objects such as the Cyrus Cylinder and the Cylinders of Nabonidus. The ea ...

and embossing. OVDs are based on

diffractive Diffraction is defined as the interference or bending of waves around the corners of an obstacle or through an aperture into the region of geometrical shadow of the obstacle/aperture. The diffracting object or aperture effectively becomes a s ...

optical structures. This gives cards the appearance of having different patterns, colours, and designs depending on the amount of light striking the OVD and the angle the OVD is viewed at.

Hologram Holography is a technique that enables a wavefront to be recorded and later re-constructed. Holography is best known as a method of generating real three-dimensional images, but it also has a wide range of other Holography#Applications, applic ...

s are a type of OVD.

References

Anti-counterfeiting {{Optics-stub