On the web. I could make the entire image clickable using code. Like the Flickr linked photos etc we get here on AP. But the QR code is designed to be scanned, generally by a smartphone, and then take your any weblink. Basically they are a barcode, that unlike supermarket goodies, links you to a webpage rather than a $$ at the checkout.
I am not sure yet if I will progress this and use it on all my images, but it is something I am testing out.
As for prints, you could, if you had a exhibition, have the QR code printed onto the print, but have a different QR code for each image. A viewer at the exhibition could scan the QR code and be taken directly to a webpage for that specific phtoo and order a print of the size they wanted, right there, at the exhibition.
I think there are a lot of people who see theses QR codes at time and who have never tried to use one. That is certainly a restricting factor, but people will try them (as you did), and at least if they understand what they do, they might, if the incentive is there, use them again.
I suppose I will not know how effective the idea can be, unless I try it.