What are these things that show up everywhere?
These are known a QR (Quick Response) codes. Originally invented by Toyota Denso Wave as a 2-D barcode for inventory tracking, this barcode format continues to evolve and expand as pattern density increases, thus allowing for more information to be stored. Information can be stored in numeric, alpha-numeric, binary, and Kanji. There are smart phone apps that can read these codes and automatically decode them or redirect you to a website for additional product information. The general structure of the encoding is shown here. The amount of information can be stored in a version 1, 2, 3, 4, 10, or 40 format, with increasing capacity with each version.
The data is encoded using the Reed-Solomon error correction algorithm with four error correction levels, with approximately 7-30% error detection/recovery depending on the level. Naturally, greater error correction capability yields lower data capacity. The use of QR Codes is free of any license and is clearly defined and published as an ISO standard. Denso Wave owns the patent rights on QR Codes, but has chosen not to exercise them.
So, you may ask how to make your own custom QR codes? Easy. Try one of these handy links:
http://qrcode.kaywa.com/ , http://goo.gl/ I prefer the Kaywa site, since it does not redirect you through the all-mighty Google first.
Be careful reading these, though, if you are not sure of the source. Malicious QR Codes combined with a permissive reader can put a computer or phone's contents and user's privacy at risk. This practice is known as "attagging". For example, the QR code can lead you to a site containing malicious software. Apparently, in Russia, a malicious QR Code caused phones that scanned it to send premium texts at a fee of USD $6 each. Ouch. If you want to go to a safe link, try the QR code in this article!
Special thanks to http://en.wikipedia.org/wiki/QR_Code for the information contained in article. -CC