How to zoom In and zoom Out image in asp.net through javascript

ASPX Code : 
 <div>
    <img border="0" src="img1.jpg" width="100"height="100"
    onmouseover="zoom('247px','268px','296px','336px',this);"
    onmouseout="zoom('47px','68px','47px','68px',this);" />
    </div>
JavaScript Java :
   <script language="javascript" type="text/javascript" >
    var nW,nH,oH,oW;
    function zoom(iWideSmall,iHighSmall,iWideLarge,iHighLarge,whichImage)
    {   
        oW=whichImage.style.width;
        oH=whichImage.style.height;   
        if((oW==iWideLarge)||(oH==iHighLarge))   
        {
            nW=iWideSmall;
            nH=iHighSmall;
        }
        else
        {
            nW=iWideLarge;
            nH=iHighLarge;
        }
        whichImage.style.width=nW;
        whichImage.style.height=nH;
    }
  </script>