.img2{
position:relative;
}
    .top {
	position:absolute;top:0;left:0;opacity:0;
      -webkit-transition: opacity 0.5s ease-in-out;
      -moz-transition: opacity 0.5s ease-in-out;
      -ms-transition: opacity .05s ease-in-out;
      -transition: opacity 0.5s ease-in-out;
    }
    .bottom{opacity:1;
      -webkit-transition: opacity .05s ease-in-out;
      -moz-transition: opacity 0.5s ease-in-out;
      -ms-transition: opacity 0.5s ease-in-out;
      -transition: opacity 0.5s ease-in-out;
     }
    .top:hover{opacity:1;}
    .bottom:hover{opacity:0;}