以下是程序代码：
script language="JavaScript"
!--
//图片按比例缩放
var flag=false;
function DrawImage(ImgD,iwidth,iheight){
    //参数(图片,允许的宽度,允许的高度)
    var image=new Image();
    image.src=ImgD.src;
    if(image.width0 && image.height0){
    flag=true;
    if(image.width/image.height= iwidth/iheight){
        if(image.widthiwidth){  
        ImgD.width=iwidth;
        ImgD.height=(image.height*iwidth)/image.width;
        }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        }
        ImgD.alt=image.width+"×"+image.height;
        }
    else{
        if(image.heightiheight){  
        ImgD.height=iheight;
        ImgD.width=(image.width*iheight)/image.height;        
        }else{
        ImgD.width=image.width;  
        ImgD.height=image.height;
        }
        ImgD.alt=image.width+"×"+image.height;
        }
    }
} 
//--
/script
调用：img src="images/topLogo.gif" onload="javascript:DrawImage(this,100,100)"