Using position

• Automatic margins, paired with values of zero for the left and right or top and bottom offsets, will center an absolutely positioned elements within its parent.

  <div class="parent">
    <img class="center" src="http://lorempixel.com/400/200/" />
 </div

  .parent {
    position: relative;
    height: 500px;
  }
  .center {
    position: absolute;
    margin: auto;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
  }