css设置图片的高等于图片的高

<div class="box">
    <img src="img/2222.jpg" />
</div>

.box {
    position: relative;
    width: 100%;
    height: 0;
    padding-bottom: 100%;
}

.box img {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
}