DataGlyph

DataGlyph is a 2D barcode system developed at Xerox PARC. DataGlyph is designed to unobtrusively integrate computer-readable information into printed materials.

Part of the Wikipedia logo as a DataGlyph code

The binary data represented by a DataGlyph is encoded with Reed–Solomon error correction. The data is interlaced and printed as a grid of 45° diagonal lines, with a downward slope representing 0, and an upward slope representing 1. These glyphs are printed very densely to the extent that they can appear as continuous, solid colors, akin to halftone.^[1] In this way, DataGlyphs can be hidden, tuned to appear similar to a particular image^[2], printed in the background of text, or presented as a decorative page border.^[3]

DataGlyphs have been incorporated into digital cards, with a data density of reportedly 3 kilobytes, much higher than magnetic stripes.^[3]