Robust, poor-man's alternative to OCR. These codes are used to track physical items, point at their use manuals, etc. Input devices: (for OLPC) integral camera; one-dimensional scanner like [http://en.wikipedia.org/wiki/CueCat CueCat ]. Some software already exists: [http://qrcode.sourceforge.jp/ Open Source QR Code Library]. (All camera cellphones in Japan bundle this function.)