A security device comprises a first diffractive structure (3) which generates a first, diffractive image or images (3A-3C) in response to incident radiation; and a second, surface relief and/or printed structure (4), having a coarser resolution than the first diffractive structure (3). The second structure (4) generates or presents a second, non-diffractive image visible in response to incident radiation, wherein the first and second images complement one another and are located relative to one another so as to define a composite representation.