By now everybody knows that it is possible to slap a logo in the middle of a QR code and — provided enough redundant data remains — the result will still be readable.
It seems it is also possible to engineer the encoded values to create a picture across the entire QR code. This technique not only produces a highly distinctive code image, it also produces completely legitimate codes.
Russ Cox calls these QArt codes, and has developed a web tool for producing them: QArt Coder. All the source code is hosted at code.google.com/p/rsc/source/browse/qr.
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