Abstract: A security device comprising a plurality of sets of nested line segments, each set comprising a plurality of line segments (52) which are specularly reflective or have a specularly reflective component formed as a relief structure in or on a surface, the sides (70) of the line segments extending at angles offset from the normal to the surface. When the line segments (52) are exposed to a light beam in an exposure direction, an image is generated different from the appearance of the line segments when viewed under different illumination conditions.