Printed Embedded Data GUIs

n7lyg writes: "Xerox PARC has come up with a way to embed data in printed images that involves using something called DataGlyphs. A DataGlyph is essentially an oblong pixel that takes the value of zero or one depending on whether it is printed angled to the left or right. Printed at sufficiently fine resolution, this is no different from ordinary offset printing effects using circular pixels, but when scanned by a computer allows recovery of arbitrary data embedded in the images or text of the printed page. An article in this month's IEEE Computer contains a lot of interesting applications of this technology, including a system to allow teachers to create printed tests and lab assignments with embedded DataGlyphs to allow automatic generation of graded and annotated results." I think we've done an article on this before, but I don't see it in the archives...