css给图片添加水印

.watermark-image {

  position: relative;

  width: 300px;

  height: 300px;

  background: url('https://timgsa.baidu.com/timg?image&quality=80&size=b9999_10000&sec=1489746806388&di=68436cfc9319b2f3afeffa9a984a2dc2&imgtype=0&src=http%3A%2F%2Fimg5.duitang.com%2Fuploads%2Fitem%2F201605%2F19%2F20160519224441_VfMWR.thumb.700_0.jpeg') no-repeat;

  background-size: 300px;

  border: 1px dotted #f00;

}

.watermark-image:before {

  content: "Message here.";

  font-size: 21pt;

  position: absolute;

  top: 50%;

  left: 50%;

  margin-left: -80px;

  background-color: rgba(255, 255, 0, 0.7);

  -webkit-transform:rotate(-45deg);

}