<p class="overimg">
    <a><img src="http://www.nowamagic.net/librarys/images/201402/2014_02_15_01.jpg"></a>
    <i class="light"></i>
</p>

.overimg{
    position: relative;
    display: block;
    /* overflow: hidden; */
    box-shadow: 0 0 10px #FFF;
}
.light{
    cursor:pointer;
    position: absolute;
    left: -180px;
    top: 0;
    width: 180px;
    height: 90px;
    background-image: -moz-linear-gradient(0deg,rgba(255,255,255,0),rgba(255,255,255,0.5),rgba(255,255,255,0));
    background-image: -webkit-linear-gradient(0deg,rgba(255,255,255,0),rgba(255,255,255,0.5),rgba(255,255,255,0));
    transform: skewx(-25deg);
    -o-transform: skewx(-25deg);
    -moz-transform: skewx(-25deg);
    -webkit-transform: skewx(-25deg);
 
}
.overimg:hover .light{
    left:180px;
    -moz-transition:0.5s;
    -o-transition:0.5s;
    -webkit-transition:0.5s;
    transition:0.5s;
}