Iād say you can try feeding the video to an Edge TOP and then to a Trace SOP which will give you geometry for the contour, and then you can use that as a particle emitter.
this could be a combination of the particlesGPU component and the opticalFlow component which both of them you can find in the Palette>Tools section of the latest TouchDesigner099.
You would have to use the output of the optical Flow as a Force on the particles - so some glsl programming would be necessary.
Perhaps something we should add as an input to the particlesGpu