.parent{
  width:100px;
  position: relative;
  border: 1px solid black;
  height: 50px;
  
}
.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;
}