title: img-responsive in Bootstrap does not work
body: <p>according to <a href="http://getbootstrap.com/css/#images-responsive" rel="noreferrer">http://getbootstrap.com/css/#images-responsive</a>, I want to make my image to support a responsive website by using </p>
  
  <pre><code>&lt;img src="..." class="img-responsive" alt="Responsive image"&gt;
  </code></pre>
  
  <p>But it is not working.</p>
  
  <p>Here is my code,</p>
  
  <pre><code>&lt;body&gt;
      &lt;img class="img-responsive" src="images/myImage.png" /&gt;
  &lt;/body&gt;
  </code></pre>
  
  <p>The original image size is <strong>284x191</strong>   </p>
  
  <p>When I open a browser on 1920*1080 screen size, the image size is <strong>284x191</strong>. But when I open a browser on 1280*720 screen size, the image size is still the same. </p>
  
  <p>I don't know what I did wrong to reduce the image size dynamically. 
  Thanks for help.</p>