title: htaccess Rewrite rule based on first two second two characters
body: <p>This should be fairly easy for all regex gurus, however we are having issues with it.</p>
  
  <p>We made a mistake by allowing people to upload images to one folders. Now we are stuck with 150k jpg images in just one folder and its slowing our server a lot.</p>
  
  <p>people are still allowed to upload to this very folder (live site) and we need to fix this slowly. the idea is to move files to subfolders like this:</p>
  
  <p><code>/jpg/121765_180x135.jpg</code>      to        <code>/jpg/12/17/121765_180x135.jpg</code></p>
  
  <p>first two/second two chars/file.jpg</p>
  
  <p>the thing is that files with less than 4 chars should stay where they are</p>