I'd just like to know if I could process webcam on OpenCV and send the instructions from a laptop to arduino in realtime by bluetooth ?
The short answer is yes, you can.
How do I achieve that?
How much of what you want to do do you need help with?
Setting up the webcam?
Getting the webcam data into OpenCV?
Processing the webcam data in OpenCV?
Sending instructions to the Arduino?
Reading the data on the Arduino?
Using the data on the Arduino?
The instructions are short.
Whatever instructions you are referring to assume, I'd guess, that you know how to do most of this, or can google for the parts you don't know how to do.