Particles conveying a code are incorporated into polymer matrix to form a core document substrate. These particles may be colored to create a distinctive look of the document that makes it unique for a particular document issuer and enables visual authentication. Addition of a covert attribute to the particle, such as a UV pigment or hidden layer of material, allows a covert, forensic characteristic and it also allows a mathematical description to be calculated describing the random distribution of a specific area on a document and then captured on it (e.g., in the bar code or magnetic stripe or digital watermark on an ID document).