Edit in JSFiddle

html {
   height: 100%;
}
h1 {
  color:white;
}
body {
  background: linear-gradient(
      rgba(0, 0, 0, 0.45), 
      rgba(0, 0, 0, 0.45)
    ),url(http://codekillr.com/wp-content/uploads/2017/02/skiing-691236_960_720.jpg);
  background-size:cover;
  background-repeat:no-repeat;
}

<h1>
Image de fond voilées
</h1>