1. A secure identification document comprising: a substrate, the substrate comprising: a substrate polymer material; and a plurality of particles, the plurality of particles comprising a non-reactive material and a covert material, wherein the plurality of particles are configured to form a random distribution within the substrate polymer material; and a machine readable data carrier within the secure identification document, the machine readable data carrier storing data, wherein a representation of the random distribution correlates to at least a portion of the data stored in the machine readable data carrier.