title: Display a .png image from python on mint-15 linux
body: <p>I am trying to display a <code>.png</code> file I constructed using the following.</p>
  <pre><code>import pydot, StringIO
  dot_data = StringIO.StringIO() 
  tree.export_graphviz( clf, out_file = dot_data,    
  feature_names =['age', 'sex', 'first_class', 'second_class', 'third_class'])
  graph = pydot.graph_from_dot_data( dot_data.getvalue())
  graph.write_png('titanic.png') 
  from IPython.core.display import Image
  Image( filename ='titanic.png')
  </code></pre>
  <p>I tried the following but neither errors nor <code>.png</code> are displayed:</p>
  <pre><code>from PIL import Image
  image = Image.open(&quot;titanic.png&quot;)
  image.show()
  </code></pre>