Optical variable device
An optical variable device or optically variable device (OVD) is an iridescent image that exhibits various optical effects such as movement or color changes. OVDs cannot be photocopied or scanned, nor can they be accurately replicated or reproduced. The OVD is often used as a security device and anti-counterfeiting measure on money, credit cards and government issued identification cards. OVDs can be created through a combination of printing and embossing.
OVDs are based on diffractive optical structures. This gives cards the appearance of having different patterns, colors, and designs depending on the amount of light striking the OVD and the angle the OVD is viewed at. Holograms are a type of OVD.