Generated by SassMeister.com.

SassMeister-input-HTML.html

<div class="background">
 
    <img class="center background-image" src="http://placehold.it/600x400">
 
</div>

SassMeister-input.scss

// ----
// Sass (v3.4.13)
// Compass (v1.0.3)
// ----


.background {
  height: 400px;
  overflow: hidden;
	position: relative;
	
	&-image {
  		background-size: cover;
  		background-position: 0 0;
  		background-repeat: no-repeat;
  		position: absolute;
  		width: 100%;
  		
  		img {
  		  width: 100%;
  		}
  }
}
 
// Utility class vertically and horizontally center thing of unknown size inside a parent of unknown size.
.center {
    position: absolute;
    top: 50%;
    left: 50%;
    width: 100%;
    text-align: center;
    -webkit-transform: translate(-50%, -50%);
    -ms-transform: translate(-50%, -50%);
    transform: translate(-50%, -50%);
}

SassMeister-output.css

.background {
  height: 400px;
  overflow: hidden;
  position: relative;
}
.background-image {
  background-size: cover;
  background-position: 0 0;
  background-repeat: no-repeat;
  position: absolute;
  width: 100%;
}
.background-image img {
  width: 100%;
}

.center {
  position: absolute;
  top: 50%;
  left: 50%;
  width: 100%;
  text-align: center;
  -webkit-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}

SassMeister-rendered.html

<div class="background">
 
    <img class="center background-image" src="http://placehold.it/600x400">
 
</div>