function starshow(1)
{
document.getElementById("ig1").style.backgroundImage='url(img/1c.png)';
}
<div id="ig1" style="width:26px;height:26px;background-image:url(img/2c.png);float:left;margin:0px;" onmouseover="starshow(1);"></div>
求解
鼠标放在div上 图片无法切换为1c.png