title: Detecting people crossing a line with OpenCV
body: <p>I want to count number of people crossing a line from either side. I have a camera that is placed on ceiling and shooting for the floor where the line is (So camera sees just top of people heads; and so it is more of object detection than people detection).</p>
  
  <p>Is there any sample solution for this problem or similar problems like this? So I can learn from them?</p>
  
  <p>Edit 1: More than one person is crossing the line at any moment.</p>