title: Clear overlay scatter on matplotlib image
body: <p>So I am back again with another silly question.
  Consider this piece of code</p>
  
  <pre><code>x = linspace(-10,10,100);
  [X,Y]=meshgrid(x,x)
  g = np.exp(-(square(X)+square(Y))/2)
  plt.imshow(g)
  scat = plt.scatter(50,50,c='r',marker='+')
  </code></pre>
  
  <p>Is there a way to clear only the scatter point on the graph without clearing all the image?
  In fact, I am writing a code where the appearance of the scatter point is bound with a Tkinter Checkbutton and I want it to appear/disappear when I click/unclick the button.</p>
  
  <p>Thanks for your help!</p>