DIGITAL WATERMARKING OF PHYSICAL OBJECTS

A machine readable indicia is formed in a blank printable medium. The indicia may be formed in an opacification layer applied to a translucent substrate, or may be formed in a laminate layer. The indicia is optically detectable from the exterior of the medium, even if the indicia is not formed on the medium's exterior surface. One particular indicia is a seemingly-random weave-like pattern of lines defined in response to (1) a first user control that determines a degree of randomness of the line(s), (2) a second user control that determines a modulation effect to be applied to the line(s), and (3) the bits to be represented thereby. Many other indicia, including checkerboards, barcodes, data glyphs, etc., can also be used.