I need some advice for choosing a camera.

I'm currently working on an installation by night where people interact with a video projection via a camera.
Here is a quick plan of the installation:

I'll need crowd movement/blob detection (no need of Kinect type detection). The position of the camera cannot be changed and It has to work with Processing1.5.1 on MacMini.

Then, do you have any suggestion on the type (or model) of camera you would use for this, considering low light? 

I've read about IR projector + IR camera but don't know how it integrates with processing?

Thanks.

http://makio.free.fr/