OPTICAL SECURITY ELEMENTS, MARKED OBJECT, METHOD OF AUTHENTICATING AN OBJECT AND USE OF OPTICAL SECURITY ELEMENTS FOR AUTHENTICATING OR SECURING AGAINST COUNTERFEITING

摘要

An optical security element made of a refractive transparent or partially transparent optical material and comprising an optical assembly of a caustic layer having a light-redirecting surface with a relief pattern of given depth and a focal length fC and an adjacent lens element of focal length fL configured to redirect incident light received from a point-like light source through it and to form a projected image containing a caustic pattern directly on a retina of an observer. A marked object, as well as a method of visually authenticating an object, and use of optical security elements for authenticating or securing against counterfeiting are also disclosed.