title: Render default image in flask
body: <p>I'm using <code>url_for</code> to generate my images url.</p>
  
  <pre><code>&lt;img src="{{ url_for('static', filename='imgs/' + images[id]) }}" &gt;
  </code></pre>
  
  <p>How to make <code>url_for</code> return <code>/static/imgs/default.jpg</code> when the requested image does not exist on the server ?</p>