title: Bootstrap 3 image responsive height not working
body: <p>I have this div:</p>
  
  <pre><code>&lt;section id="categorias"&gt;
   &lt;div class="container content-section"&gt;
    &lt;div class="row"&gt;
       &lt;div  class="col-md-3"&gt;
          &lt;img class="img img-responsive" src="img/catmusica.png"&gt;&lt;/img&gt;
       &lt;/div&gt;
       &lt;div class="col-md-3"&gt;
          &lt;img class="img-responsive" src="img/catpaisajes.png"&gt;&lt;/img&gt;
       &lt;/div&gt;
       &lt;div class="col-md-3"&gt;
          &lt;img class="img-responsive" src="img/catgrafiti.png"&gt;&lt;/img&gt;
       &lt;/div&gt;
       &lt;div class="col-md-3" &gt;
          &lt;img class="img-responsive" src="img/catpoly.png"&gt;&lt;/img&gt;
       &lt;/div&gt;
    &lt;/div&gt;
  &lt;/div&gt;
  &lt;/section&gt;
  </code></pre>
  
  <p>That looks like this:
  <a href="https://i.stack.imgur.com/qKVgs.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qKVgs.jpg" alt="enter image description here"></a></p>
  
  <p>And I want to maintain the 4 columns or at least 2 above and 2 below when I shrink the window but this happens:
  <a href="https://i.stack.imgur.com/TiI4Q.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/TiI4Q.png" alt="enter image description here"></a></p>
  
  <p>I have only bootstraps css.</p>
  
  <p>Thanks</p>