Optically variable devices (OVDs) are security features used to prevent counterfeiting and fraud. They change appearance when viewed from different angles, making them difficult to replicate. Common examples include holograms, color-shifting inks, and microprinting, which are often found on banknotes, credit cards, and identification documents. These devices rely on optical effects to create a dynamic visual experience. When light interacts with the materials used in OVDs, it produces varying colors and patterns. This technology enhances security by making it easier to identify authentic items while deterring counterfeiters from creating convincing replicas.