Jeremy’s written a great roundup of Papercamp, which I wasn’t able to get to. Amongst other things, he says this:
everyone gathers around a laptop for a demo from Durrell Bishop and Tom Hulbert from Luckybite. They have a printed book based on their music collection. Each page of the book contains an image—usually an album cover—and a barcode. If you scan the barcode from a page in the book, the corresponding music will play on your computer (or your phone). The book is the UI. The wireless barcode reader is where the magic happens. If these guys can make a cheap version of this reader, it will fantastic …for all us. Right now the only expensive bit is the reading head but the price could come down as low as a dollar or two.
Surely webcams and QR codes (or variants) are the cheap route here?