div.firstpic {
  position:absolute;
  z-index:3;
  top:175px;
  left:15px;
}

div.secondpic {
  position:absolute;
  top:260px;
  left:105px;
  z-index:2;
}

div.thirdpic {
  position:absolute;
  top:375px;
  left:35px;
  z-index:1;
}

img {
  border:2px solid black;
}