Using QR Codes for Mobile Tagging has some pitfalls, that you should definitely avoid.

QR Code with 20 characters




QR Code with 80 characters




QR Code with 200 characters




QR Code with 400 characters



Pitfalls:

Using QR Codes for Mobile Tagging has some pitfalls, that you should definitely avoid.

Most problems arise because the tester has a good phone (like Nokia's N95) with a high quality camera, but the actual user has an average phone with an average camera.


Whitespace / Quitezone:

Make sure you leave an empty space of around 4 modules on each side.


Amount of data:

You should not encode more than 60 characters in a QR Code. Otherwise detection will be too bad with average phones (see "Capacity").


Color:

You should always use black and white. If contrast is too low code detection will be impossible.


Design:

Some people add logos in the middle or change colors. You should not do that (although it looks very cool) as detectability goes down and people will have difficulties to recognize it as a QR Code.


Size:

The code should never be smaller than 2cm (with ~40 characters encoded). The more characters you encode the larger the code has to be. But you should never encode more than 80 characters.

And here is exactly, how one should NOT do it (because the code is far too small..., and there is not enough empty space of around 4 modules on each side.):
http://a1.twimg.com/profile_background_images/60295168/Twitter_Background.JPG
Average phones with an average cameras, may not be able to scan your code properly..., Justin.
He is not thinking mainstream friendly. Telnic never was thinking very mainstream friendly. Quasi only tech savy users and developers, had a chance to understand .Tel and all its features.

Link and source:
http://www.beetagg.com/BeeTaggSystem/qrcode.aspx


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