In my opinion it is obnoxious that QR codes have to be square
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The finder pattern and error correction bits mean you can deviate a lot from the standard squares. It works best if you don't do that but low density QR codes are so quick/easy/reliable to scan even with mediocre implementations that you can get away with a lot of evil.
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Most QR codes use the lowest level of error correction but if you turn it up to the highest level, it can cope with 30% of it being covered / cropped away. Can also get away with sticking fake data around the edges, especially if you don't do all of them. Can happily use circles.
It's not nearly as bad as some companies deciding to deviate from using black/white. The particularly evil ones combine that with inverting the colors for no apparent reason along with overlaying their logo on top of it. Good QR scanners already cope with far worse than circles.
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