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<!-- IE10+, FF, Chrome, Safari, Opera -->
<div class="panel">
    <div class="front card">
        <img src="http://placehold.it/300x300&text=front">
    </div>
    <div class="back card">  
        <img src="http://placehold.it/300x300&text=back">
    </div>
</div>

.panel {
    position: relative;
    width: 300px;
    height: 300px;    
}

.card {
    position: absolute;
    top: 0px;
    left: 0px;
    width: 100%;
    height: 100%;
    -o-transition: all .5s;
    -ms-transition: all .5s;
    -moz-transition: all .5s;
    -webkit-transition: all .5s;
    transition: all .5s;
    -webkit-backface-visibility: hidden;
    -ms-backface-visibility: hidden;
    -moz-backface-visibility: hidden;
    backface-visibility: hidden;
}

.front {
    z-index: 2;
}

.back {
    z-index: 1;
    -webkit-transform: rotateY(-180deg);
    -ms-transform: rotateY(-180deg);
    -moz-transform: rotateY(-180deg);  
    transform: rotateY(-180deg);  
}

.panel:hover .front {
    z-index: 1;
    -webkit-transform: rotateY(180deg);
    -ms-transform: rotateY(180deg);
    -moz-transform: rotateY(180deg);
    transform: rotateY(180deg);
}

.panel:hover .back {
    z-index: 2;   
    -webkit-transform: rotateY(0deg);
    -ms-transform: rotateY(0deg);
    -moz-transform: rotateY(0deg);
    transform: rotateY(0deg);
}