SOURCE

<div class="box">
  <img src="http://www.yuanyouliang.com/assets/img/Coding.png" alt="" class="center" />
</div>

.box {
  background-color: #ccc;
  position: relative;
  height: 200px;//必须
}
.center {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}