A CodePen by Ana Tudor. Sliding door effect (box-shadow method) - Same effect as http://codepen.io/html5web/pen/EFyzB and http://codepen.io/thebabydino/pen/Kkvum

index.html

<div class='s s1'></div>
<div class='s s2'></div>
<div class='s s3'></div>
<div class='s s4'></div>

style.css

body { background: dimgrey; color: silver; text-align: center; }
.s {
  display: inline-block;
  margin: 1em;
  width: 12.3em; height: 5.9em;
  border-radius: .35em;
  background:    url(http://imgsrc.hubblesite.org/hu/db/images/hs-2007-16-e-small_web.jpg) 0 50%;
  transition: .85s;
  cursor: pointer;
}
.s1 {
  box-shadow: 0 0 .35em black, 0 0 0 .5em, 
    inset 12.3em 0;
}
.s2 {
  box-shadow: 0 0 .35em black, 0 0 0 .5em, 
    inset 0 6em;
}
.s3 {
 box-shadow: 0 0 .35em black, 0 0 0 .5em, 
    inset -12.3em 0;
}
.s4 {
  box-shadow: 0 0 .35em black, 0 0 0 .5em, 
    inset 0 -6em;
}
.s:hover {
  box-shadow: 0 0 .35em black, 0 0 0 .5em, 
    inset 0 0;
}