The invention relates to a holographic viewing device that enable printing or the like to be directly applied to a transmission hologram substrate without recourse to any frame for supporting and reinforcing a transmission hologram, thereby simplifying construction while enhancing aesthetic and decorative attributes, and a holographic viewing card incorporating it. The holographic viewing device enables a given image or message to be viewed near the positions of point light sources upon viewing the point light sources through a hologram, and comprises a transparent substrate 41, a hologram-formation layer 42 and a printing layer 45. The hologram-formation layer 42 may be any one of a phase type diffractive optical element having a relief structure 43 on its surface, a phase type diffractive optical element having a refractive index profile in its layer, and an amplitude type diffractive optical element having a transmittance profile in its layer.

A method and system for forming a holographic structure in a material. The holographic structure is configured to project a selected target image in the far field under illumination of the holographic structure by a laser. The method calculates a modified design for the holographic structure that encodes a unique identifier within the holographic structure for projecting the target image. The method modifies the material by mapping features corresponding to the modified design into the material so as to form the holographic structure. A basic check of the authenticity of the material is performed by checking whether a projected replica of the target image is as expected. A more detailed check of the authenticity of the material is performed by directly inspecting the features in the holographic structure.