The term ‘hologram’ is generally used to identify optical devices that work on the basis of variable diffractive images (diffractive optical variable image devices, or DOVIDs).

Holograms are true optical devices: the visual effects of the images they show change as the lighting and viewing angle vary. It is precisely by varying the viewing angle that three-dimensional images are created. 

Holograms are created using a photographic technique that records the light scattered from an object and then presents it in a way that appears three-dimensional (holography). Holograms cannot be reproduced by colour printers, scanners or cameras. Their complexity can be increased by inserting several images and effects. 

Holograms have several fields of application, from visual arts and decoration to security. In the field of anti-counterfeiting, holograms are used to authenticate products. Successful authentication of a hologram requires knowledge of the original hologram, which is used as a comparison. Any difference between the two could mean that the hologram being examined might be counterfeit, and so each change or update needs to be considered.