.responsive-container {

    position: relative;

    width: 100%;

    border: 1px solid black;

}

​

.dummy {

    padding-top: 100%; /* forces 1:1 aspect ratio */

}

​

.img-container {

    position: absolute;

    top: 50%;

    left: 50%;

}

​

.img-container > img {  

  margin-top:-50%;

  margin-left:-50%;

}

img {

  width:300px;

  height:300px;

  background-color:red;

}