There’s an interesting post about QR codes on public transport on renaissance chambara and how they’re not very effective. You often can’t get close enough to them, you’ll rock about too much to get a still picture and even if you do capture it you’re probably undergound and therefore have no mobile signal.
It’s a good point as these codes are showing up more and more on London Underground trains which spend a lot of their time, well, undergound when in central London. This is especially true of the deep level tube lines like the Jubilee, Piccadilly, Central, Northern, Bakerloo and Victoria which are quite a way below the surface for their busiest sections.
I’d like to add an additional problem that I’ve encountered. It wasn’t on public transport – it was in the toilets at a cinema, actually – but an advert for a book had a QR code to let you enter a competition. Problem was, the QR code pointed to a page on Facebook, which wasn’t available on Facebook Mobile – which is what Facebook defaults to when on a mobile handset, obviously.
So that’s another thing to bear in mind – people will use mobiles to read the codes and therefore your page should be easily readable by mobile clients. In particular, the pages shouldn’t use Flash (as iPhone users won’t be able to read them) and should preferably use a mobile edition that displays properly on small screens.
I’ve also seen a code which uses Microsoft Tag – I wonder how many people tried to scan it with a standard QR reader and wondered why it didn’t work?