鼠标滑动导致图片从模糊转清晰的效果

<img src="http://lh3.google.com/yedsky/RfTTorxo0qI/AAAAAAAAABE/T2h_YX8e6lg/1.jpg" alt="模糊变清晰" style="filter:alpha(opacity=50)" onmouseover="this.filters.alpha.opacity='100'" onmouseout="this.filters.alpha.opacity='50'" />

效果如下