According to a first aspect of the invention, there is provided a method of deriving information from an optically readable security element, the method comprising: optically reading the optically readable security element, the optically readable security element comprising one or more optically readable structures, optically readable in response to excitation of the one or more optically readable structures, the one or more optically readable structures being arranged to interact with one or more proximal structures of the optically readable security element, the interaction being such that an excitation-emission relationship for the one or more optically readable structures interacting with the one or more proximal structures, is different to an excitation-emission relationship for the one or more optically readable structures and the one or more proximal structures in isolation; the reading comprising: determining data indicative of an optical property of the optically readable security element using first emission electromagnetic radiation, emitted in response to first excitation of the one or more optically readable structures; and deriving the information from the determined data.