title: people detection with haar cascade
body: <p>I am working on a project in my school to detect how many students are in the classroom. Like in this picture.
  <img src="https://i.stack.imgur.com/fchk5.jpg" alt="classroom"></p>
  
  <p>I have been trying to use Haar Cascade in opencv for face detection to detect people, but the result is very bad. Like this:
  <img src="https://i.stack.imgur.com/PALba.jpg" alt="After detection"></p>
  
  <p>I took thousands of pictures in classroom, and cropped the picture with people manually. There are about 4000 positive samples and 12000 negative samples. I was wondering what did I do wrong?
  When I crop the image, should I only crop only head like this?
  <img src="https://i.stack.imgur.com/2c6x1.png" alt="Head">
  Or like this with body?
  <img src="https://i.stack.imgur.com/5mCDB.png" alt="With Body"></p>
  
  <p>I think I had enough training samples, and I follow the exact procedure with this post:
  <a href="http://note.sonots.com/SciSoftware/haartraining.html#v6f077ba" rel="nofollow noreferrer">http://note.sonots.com/SciSoftware/haartraining.html#v6f077ba</a>
  which should be working.
  Or should I use a different algorithm like HOG or SVM. Any suggestion would be great for me, I have been stuck in this for months and don't have any clue. Thanks a lot!</p>