.parent{
  width:400px;
  position: relative;
  
}
.inner {
  padding-top:100%;
  position: relative;
  width:100%;
  height:100%;
}

img{
  width:100%;
  position:absolute;
  top: 0;
  right:0; 
  bottom:0;
  left:0;
  margin:auto;
}