How does this tracker work?

[janhuang6]

My questions may be dumb. I want to know how this tracker finds the person to track in the very first frame? Why it needs groundtruth.txt for all the frames as input? I want to use this tracker on my own video, how could I generate the groundtruth.txt? Or if I have already known the ground truth for every frame, why do I still need this tracker? Thanks! Jan