A security device is disclosed, comprising: a surface relief structure formed of a cured material, the cured material comprising a binder and dispersed therein at least a first pigment having a first detection characteristic. The surface relief structure is configured such that part(s) thereof have dimensions sufficient to accommodate a first concentration of the first pigment and other part(s) have dimensions too small to accommodate the first concentration of the first pigment, and preferably too small to accommodate substantially any of the first pigment. The detection characteristics of the cured material vary across the surface relief structure in accordance with the dimensions thereof.