OPTICAL READING OF A SECURITY ELEMENT

According to a first aspect of the present invention, there is provided a method of determining a unique identifier for a security element, the method comprising: optically reading the security element, the security element comprising a number of emitters that are each capable of exhibiting a different emission response to excitation of the number of emitters; the reading comprising determining data indicative of an optical property of the security element using first emission electromagnetic radiation, emitted in response to first excitation of the number of emitters, and determining data indicative of an optical property of the security element using second emission electromagnetic radiation, emitted in response to second, different, excitation of the number of emitters; and the unique identifier being determined from a map of a variation in determined data indicative of an optical property with respect to the excitation of the number of emitters.