Render QR codes with Rails 3 by the rqrcode-rails3 will generate QR codes.But when you use chunky_png gem that create the image in png format by use of the QR code which generated by the rqrcode-rails3. And now when you scan the png which created by chunky_png gem from any devise which scan the QR code will give you nonthing in output. So better use it with the Mini_magick gem that support rqrcode-rails3 and save the image where you want for full step by step solution http://bharatsonis.wordpress.com/