This only works when people are separate enough so they have an individual silhouette. If doing length of line tracking however, it becomes much more tedious, with edge detection necessary and such. Also, if using a 360 camera, this becomes more complex, as a person in the middle blob shape would be completely different from a person at the edge. I am aware you can use a filter, but it cuts out some area sometimes.

This is a surprisingly hard problem that I've explored before. Feel free to email me about it!