.img {
	display:block;
	position: relative;
	width:800px;
	height:450px;
	margin:0 auto;
}
.img:before {
	content: "";
	position: absolute;
	width:200px;
	height: 100%;
	top: 0;
	left: -150px;
	overflow: hidden;
	background: -moz-linear-gradient(left, rgba(255,255,255,0)0, rgba(255,255,255,.2)50%, rgba(255,255,255,0)100%);
	background: -webkit-gradient(linear, left top, right top, color-stop(0%, rgba(255,255,255,0)), color-stop(50%, rgba(255,255,255,.2)), color-stop(100%, rgba(255,255,255,0)));
	background: -webkit-linear-gradient(left, rgba(255,255,255,0)0, rgba(255,255,255,.2)50%, rgba(255,255,255,0)100%);
	background: -o-linear-gradient(left, rgba(255,255,255,0)0, rgba(255,255,255,.2)50%, rgba(255,255,255,0)100%);
	-webkit-transform: skewX(-25deg);
	-moz-transform: skewX(-25deg)
}
.img:hover:before {
	left: 150%;
	transition: left 1s ease 0s;
}

<a href="#" class="img"><img src="http://img.loveqiao.com/pic1.jpg" width="800"></a>