Simple object recognition in webcam stream

Hello,
I would like to create an app that is able to detect personnal QRcode in a webcam stream. This app should allows people in a room to vote by showing his own QRcode card at the camera. The orientation of the card will give the reply (4 possibilities).
I imagine a simple QRcode, framed by a shape like this
image
So the app has to localise this shape everywhere in the camera image, and then decode the QRcode inside this shape (not represented here).
I work in C#. I think tha OpenCV could be a good solution.
Does someone know a tuto which explain me how to do ?
Thanks a lot.

Chris (sorry for my english)

And I add that in my scene, the cards might have different size rotation and tilt, like that :