QR Code Generation for the Products - by Google API
It's very simple to generate qr code for product page. You can modify size and quanlity of QR code:

- chs - Size of the image in pixels, in the format <width>x<height>
chs=<width>x<height>

- chl - The data to encode.

- choe=<output_encoding>

- Error correction Levels: H = 30%, Q = 25%, M = 15%, L = 7%
chld=L or ...

Demo: http://nextlevel.com.vn/