(sorry for windows users but it is quite the same)
Then you can find some algorithm which can detect your face or some couloured shape. (search Haar detect in google)
Once you made that works on your computer with your webcam, go buy a raspberry pi and a webcam.
OpenCV does work with python so it should be straight forward to convert your C code into Python.
Finally you have to learn how to communicate between your Raspberry and your quadrotor controller, it use some kind of wierd protocols used in RC remote controller.
On that point I can't help since I have never tried this out yet.
Not sure exactly what you are wanting but have you considered using a setup that works somewhat like smart missiles use, where an infrared spot is pointed at the target and a camera just has to keep track of that spot.
I have thought about this before to get a pro video camera to track a scene by having either a infrared spot project on the target or have a somewhat concealed infrared LED on the target. A low res. camera able to see the infrared or perhaps a matrix of infrared sensors can be used to do the tracking. The infrared can be distinguished from other stray infrared perhaps by making it pulse at a set rate.
