只用CSS就可实现容器内图片上下左右居中

.main{ width:600px; height:400px; margin:100px auto;text-align:center;vertical-align:middle;display:block;position:relative; background:#ddd;}
.main a{display:table-cell;vertical-align:middle;width:600px; height:400px; }
.main a img{max-width:600px;max-height:400px; }