title: Drawing circles on image with Matplotlib and NumPy
body: <p>I have NumPy arrays which hold circle centers.</p>
  <pre><code>import matplotlib.pylab as plt
  import numpy as np
  npX = np.asarray(X)
  npY = np.asarray(Y)
  plt.imshow(img)
  // TO-DO
  plt.show()
  </code></pre>
  <p>How can I show circles at the given positions on my image?</p>