1. = http://delivr.com/2apba_qr 2. = http://cellphonia.org/toronto/ 3. = http://cellphonia.org/toronto/ 4. = http://cellphonia.org/toronto/ 5. = http://cellphonia.org/toronto/My testing method was provided by QR4 - thank you. Beyond the obvious sneaky redirect in result 1 the explanation of the differences is found in this discussion thread from stackoverflow.com. The variable seems to be the error-detection algorithm.
From my investigation I recommend GoQR.me as they give you control over the QR code parameters mentioned in the stackoverflow thread.
Note the URLs of the "free" QR code generator websites in the QR file name of the .PNG
Wikipedia writes about the QR code standard.
SONic Geography runs April-May, 2013 via NAISA.ca Toronto CANADA.