还是很搞，有点弄不明白

* {

    margin: 0 auto;

    padding: 0;      

}

div{width: 500px;height: 270px;border:10px solid rgba(0,0 ,255,.25);

background:url(http://img1.sycdn.imooc.com/climg//582c342b0001fd6507000210.jpg) no-repeat;

background-size: cover;

    padding: 10px;

background-clip:padding-box;

}

div:hover{background: url(http://img1.sycdn.imooc.com/climg//582c34220001091605000150.jpg) no-repeat 10px 10px;

background-size: cover;

background-clip: border-box;

background-origin: content-box;

}