data squares (denser than a Barcode ) > http://www.denso-wave.com/qrcode/qrfeature-e.html

“With Semapedia you can hyperlink your physical world with knowledge that matters. To do this you create small Semapedia Tags consisting of a cell-phone readable 2D Barcode that will link others to the content you provide. Or put simply: Mark things like buildings, books, airplanes, cars or whatever with small Semapedia Tags that let others be a entry-point for more information.” http://www.semapedia.org/