title: HTML/CSS/jQuery: background-image opacity
body: <p>Let's say I have a div, and that div should have a background-image:url(foobar.png). Also, however, foobar.png's opacity should be set to 40% so that the background image is translucent. How can I do this?</p>
  
  <p>If this is not possible without JavaScript, is there an example script I can refer to? Something like this?</p>
  
  <pre><code>jQuery.fn.fadedBgImg = function(url, opacity) {
  
      // Create block element that fills `this` element
  
      // Set z-index of said element to lowest
  
      // Set opacity of said element to 40%
  
      // Insert said element into parent
  }
  </code></pre>