title: Insert a string before the extension in a filename
body: <p>How can I insert a string before the extension in an image filename? For example, I need to convert this:</p>
  
  <pre><code>../Course/Assess/Responsive_Course_1_1.png
  </code></pre>
  
  <p>to this:</p>
  
  <pre><code>../Course/Assess/Responsive_Course_1_1_large.png
  </code></pre>