title: What's difference between np.zeros(img) and np.copy(img)*0?
body: <p>What is the difference between these three:</p>
  
  <p><code>np.zeros(img)</code>, <code>np.zeros_like(img)</code>, and <code>np.copy(img)*0</code>?</p>
  
  <p>When should I use each of them?</p>