I need to make a camera react to movement and show the image on a 'mirror'.
React in what way? Is the Arduino to sense the movement? It won't be involved in getting the camera image to the monitor.
Ideally I would like the camera to track the person if he/she moves
If there is nothing that the person wears that can be tracked, this is not possible.
The camera could be connected to a computer that can do image processing, and compute how that image is moving.
How that transformation data is of any use/interest to the Arduino is not clear, though.