In case anyone else is interested in the contrast tolerance it seems that two colour QR codes don't work very well (I've tried a few other colours in addition to the ones here, might try very pale grey for completism!). The ones with a yellow oval next to it worked when using ScanLife for iPhone - it takes you to our homepage at http://www.chi-med.ac.uk
|Possibly if the green and white one on the bottom right had a boundary around it that would help, dunno.|
Mildly tempted to swap bits around and see which bits of the image are essential and which can be tweaked with no loss of function.
This QR code below works fine - it has a white boundary and fairly good contrast (assume it's sufficient to be machine readable) although I'm sure I'd be confused by the image behind it.