Abstract: Embodiments of the invention, therefore, provide improved systems and methods for tracking targets in a simulation environment. A security device having a first layer that carries indicia arranged to present covert information. Embodiments of the invention may include a second layer that carries decoding optical elements. In some embodiments, the second layer is arranged to be moveable relative to the first layer from a first position to a second position. In some embodiments, when in the second position, the optical elements serve to cooperate with the indicia so as to reveal the covert information for visual observation.

Abstract: A security device includes an array of microimages which, when viewed through a corresponding array of substantially spherical microlenses, generates a magnified image. In some cases, the array of microlenses is bonded to the array of microimages.

Abstract: A security device includes first and second diffractive structures contained within a surface relief structure. The structures are such that the device responds to illumination at a first, visible wavelength to generate a first, visible pattern while any pattern generated by the second structure is not substantially visible at that wavelength, and the device responds to illumination at a second wavelength substantially different from the first wavelength to generate a second pattern suitable for machine reading while any pattern generated by the first structure is substantially suppressed relative to the machine readable pattern at that wavelength.