One of my hobbies is looking for QR codes by leafing through the free papers which blight the city of London. Yes, I lead a tragic existence, but it keeps me off the streets - so let me be, eh?
Most of the QR codes that I see now are pretty good. They have clear explanatory text, point to mobile websites, and generally follow the Ten Commandments for QR codes.
But, every so often I spot one which really shouldn't have been let out in the wild. A property company (who shall remain nameless to spare their blushes) printed this QR code at the bottom of an advert - beside the logos showing how green and ISO compliant they are.
Wow! It's not that I have monster-sized fingers - that QR code really is tiny.
Let's zoom in and take a look at what the newspaper printing process has done to the code.
As we can see, the printing resolution just isn't sufficient for a code as tiny as this. The fragile pixels become an inconsistent mess, straight lines go wobbly, and the ink bleeds into the whitespace.
QR codes need unambiguous pixels with a clear delineation between content and space. Lines need to be straight, squares need to be square, and the contrast between colours needs to be high. This QR code fails on all levels.
Even if this code had been laser printed onto premium white paper, it would still be too small for many cameras to scan. It would require a macro focus that is lacking in all but high end devices.
One of the most important rules of QR codes is simply "test". This code just doesn't work. It could lead to the greatest mobile experience known to humanity - but if a user can't actually get to it, all is for naught.