Shaded trailed particles emitted from video in

Just staring experimenting for an event first week of June.
Started from the Particles based video processing template, I attached a Video in source so to get a video feed from a camera, and got this kind of basic setup (using my hand)
Particles based video processing
Looking at some tutorials I wanted to ask some hint about

  • Have the particles only outside the moving shape
  • Have them emitted only from the edges of the shape and not all the image
  • have them trails and shading like in this short tutorial
  • using optical flow I can track the movements respect the background, but what if I will project behind a performer moving on the stage? I suppose the system will capture also his own projected video movements. Apart using stereo cameras, there is any other solution to avoid this.