<div class="container">
  <img src="http://tympanus.net/codrops-playground/assets/images/cssref/properties/mask-mode/wheat.jpg" alt="">
</div>
body {
  color: #555;
  font-size: 1.1em;
  font-family: 'Helvetica Neue', Helvetica, Arial, sans-serif;
}

p {
  margin: 100px 0;
}

.container {
  margin: 40px auto;
  max-width: 600px;
}

img {
  display: block;
  width: 100%;
  height: 450px;
  margin: 50px auto;
  -webkit-mask-image: linear-gradient(black, purple, yellow, transparent);
  mask-image: linear-gradient(black, purple, yellow, transparent);
  -webkit-mask-mode: luminance;
  mask-mode: luminance;
}