Camera Based Movement Detection

We are developing camera-based position holding algorithm, need to hold horizontal and altitude position using downward facing camera. We ourselves can do feedback loop controls, but need someone to assist on camera based movement detection, generating horizontal and vertical movement error signal for PID control. Some requirements are: 1. Using low cost camera module 2. Simple interface to microcontroller 3. Software runs on low cost 32bit microcontroller To select candidate for the job, we’ll need to know below information beforehand: 1. Which model camera module would you suggest to use? We’ll need to check price beforehand. 2. What data RAM and program Flash size do you think needed? 3. With 100MHz RISC and FPU, how many image comparisons results per second do you think can be achieved? Graduate student with image processing experience welcome.