图片自适应单元格大小

我想以m行n列的方式显示图片，采用了table的方式，table充满整个页面。但是现在有个问题，就是图片高度过大撑破单元格。<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head><title>
图片列表行列分布
</title>
<style type="text/css"> 
html,body,form,table   { 
margin:0; 
width:100%;
height:100%; 
} 
</style>
</head>
<body>
    <form  id="form1" action = "" >        
        <table id="lvwAdver_tbLayout" >    
            <tr id="lvwAdver_ctrl0_trGroup">
                <td id="lvwAdver_ctrl0_Td1_0" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl0_Td1_1" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl0_Td1_2" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
            </tr>
            <tr id="lvwAdver_ctrl1_trGroup">
                <td id="lvwAdver_ctrl1_Td1_3" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl1_Td1_4" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl1_Td1_5" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
            </tr>
            <tr id="lvwAdver_ctrl2_trGroup">
                <td id="lvwAdver_ctrl2_Td1_6" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl2_Td1_7" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl2_Td1_8" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
            </tr>
            <tr id="lvwAdver_ctrl3_trGroup">
                <td id="lvwAdver_ctrl3_Td1_9" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl3_Td1_10" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
                <td id="lvwAdver_ctrl3_Td1_11" >
                    <img src="北京1.jpg" style="z-index:-100; width:100%; height:100%;" />
                </td>
            </tr>
        </table>       
    </form>
</body>
</html>