title: Background image in a python plot
body: <p>I need to plot over an image. I use this code to display the image:</p>
  
  <pre><code>plt.figure()
  mngr = plt.get_current_fig_manager()
  fname = 'erausal-valence.jpg'
  image = Image.open(fname).convert("L")
  arr = np.asarray(image)
  plt.imshow(arr)
  </code></pre>
  
  <p>Over on this image I need to plot an array build with components:</p>
  
  <pre><code>for i in range(0, len(BPM)):    
      for k in range(0, len(BPM)):
          (X[k], Y[k]) = pol2cart(BPM[k], -SC[k]);
          plt.plot(X[k], Y[k])
  </code></pre>
  
  <p>but plot shows the image and doesn't show the plot of the X and Y arrays.</p>