div {
  background-image:
     url(kittens.jpg);
}
div:after {
  content: '';
  top:0; bottom: 0;
  left: 0; right: 0;
  position: absolute;
  background-image:
     url(iphone_mask_large.jpg);
  -webkit-mask:
     url(iphone_mask_mask.png);
}

JPG | Mask PNG