gistfile1.html

<!-- this one works, but ugly in IE7 -->
<div style="width:220px;text-align:center">
<a href="#">
<img src="foo16.png" />
</a>
</div>

<!-- this one not works in IE8 standard mode -->
<div style="width:220px;text-align:center">
<a href="#">
<img src="foo16.png" style="display:block" />
</a>
</div>

<!-- this one should works -->
<div style="width:220px;text-align:center">
<a href="#">
<img src="foo16.png" style="display:block;margin:0 auto" />
</a>
</div>

see also: http://w3help.org/zh-cn/causes/RT8003