Edit in JSFiddle

div {
  position: relative;
  display: inline-block;
  overflow: hidden;
}

div:before,
div:after {
  position: absolute;
  top: 0;
  left: -30px;
  width: 50%;
  border-top: 30px solid;
  border-right: 30px solid transparent;
  color: white;
  content: '';
}
div:after {
  right: -30px;
  left: auto;
  border-right: none;
  border-left: 30px solid transparent;
}

<div>
    <img src="http://placekitten.com/200/300">
</div>