title: How to write PNG image to string with the PIL?
body: <p>I have generated an image using <a href="http://www.pythonware.com/products/pil/" rel="noreferrer">PIL</a>. How can I save it to a string in memory?
  The <code>Image.save()</code> method requires a file.</p>
  
  <p>I'd like to have several such images stored in dictionary.</p>