/* presuming that the a element has a background image */
.grid .column a {
width: 100%;
overflow: hidden;
display: block;
/* scale the image proportionally based on the elements height and width */
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
/* make the elemnts height a 1:1 ratio with it's width */
height: 0;
padding-bottom: 100%;
}