See the Product Overview video on the page for the Computer Vision System Toolbox. http://www.mathworks.com/products/computer-vision/ In that movie there are several demonstrations of how you can track objects, including people. So you can do it with that toolbox, which probably comes with demos for tracking.
I'm not sure if that's what you meant when you said " the code of model 'People Tracking' in matlab 2012", which sounds like you have in mind some particular script that you saw demonstrated somewhere. Or possibly some Simulink model that you saw demonstrated that was specifically called "People Tracking."
