How can I make my own custom codes?
I made three QR codes of the information using generators from Qurify, the University of Bath QR code generator and the Nokia QR code generator. Note that although similar, they are not the same:
Compare the different codes. Some parts of a QR code are sacrosanct, so leave these alone:
After that, it's a process of trial and error with Photoshop to introduce the additional information you want into the redundant areas.