Code a particle filter to track the location and size of a filled circle

I would like an algorithm coded in python that implements a particle filtering algorithm to track the location (x,y coordinate) and size (pixel radius) of a dark circle that moves and changes size on a lighter background using the grey-level-differences contour model in the attached paper. (note that the attached paper uses an ellipse rather than a circle; for my purposes the simpler circle model is sufficient).