<div class="item">
  <div class="col-md-4">
    <div class="row">
      <div class="col-md-12"><a href="#"><img src="http://placehold.it/500x250/993399/fff&text=7_1" class="img-responsive"></a></div>
    </div>
    <div class="row">
      <div class="col-md-12"><a href="#"><img src="http://placehold.it/500x250/339933/fff&text=7_2" class="img-responsive"></a></div>
    </div>
  </div>
</div>