title: Django save image from url and connect with ImageField
body: <p>I have in <code>models.py</code>:</p>
  
  <pre><code>class Item(models.Model):
      image_file = models.ImageField(upload_to='images')
      image_url = models.URLField()
  </code></pre>
  
  <p>I want django automatically download and locally save image from <code>image_url</code> and "connect" it with <code>image_file</code></p>
  
  <p><strong>How it should act:</strong></p>
  
  <ol>
  <li>I Paste <code>https://docs.djangoproject.com/s/img/site/hdr_logo.gif</code>
  into <code>image_url</code> field in admin</li>
  <li>Click "save"</li>
  <li>In templates write <code>&lt;img src="{{ item.image_file.url }}"&gt;</code>. It shows
  image from my server, not <code>djangoproject.com</code></li>
  </ol>
  
  <p><strong>What I've tried:</strong></p>
  
  <p>I've overwritten <code>save</code> method of <code>Item</code> class. I saved image locally via <code>urllib</code>, but I am stuck on connecting this saved image with <code>image_file</code> field</p>