切图全在

<div class="img-container">
<div class="img-left"></div>
<div class="img-right"></div>
</div>
<style>

.img-container{
position: relative;
width: 200px;
height: 100px;
border:solid 4px red;
}

.img-left{
background: url(http://demo.imatlas.com/img/left.jpg);
background-size: cover;
width: 100%;
height: 100%;
}

.img-right{
position: absolute;
left: 0;
top: 0;
background: url(http://demo.imatlas.com/img/right.jpg);
background-size: cover;
-webkit-mask-image: -webkit-linear-gradient(left top, transparent 50%, white 50%);
width: 100%;
height: 100%;
}</style>