title: Apache show a default image when there is a 404 error under a specific URL pattern
body: <p>In a pure client based web app I need to show a background image that sometimes doesn't exist. Is there a way of 'forcing' Apache to serve an image when a specific URL pattern returns a 404 error?</p>
  
  <p>The URL pattern that might return a 404 is:</p>
  
  <p><a href="http://host/assets/user-images/xxxxx.jpg" rel="nofollow">http://host/assets/user-images/xxxxx.jpg</a> </p>
  
  <p>Where I want to serve the image:</p>
  
  <p><a href="http://host/assets/user-images/default.jpg" rel="nofollow">http://host/assets/user-images/default.jpg</a> </p>
  
  <p><strong>NOTE:</strong></p>
  
  <p>I already use a .htaccess</p>
  
  <pre><code>RewriteEngine On
  RewriteCond %{REQUEST_FILENAME} !-f
  RewriteCond %{REQUEST_FILENAME} !-d
  RewriteRule ^ index.php [QSA,L]
  </code></pre>