image hover transition in out
#cf {
position:relative;
height:281px;
width:450px;
margin:0 auto;
}
#cf img {
position:absolute;
left:0;
-webkit-transition: opacity 1s ease-in-out;
-moz-transition: opacity 1s ease-in-out;
-o-transition: opacity 1s ease-in-out;
transition: opacity 1s ease-in-out;
}
#cf img.top:hover {
opacity:0;
}