var flag=false;
function DrawImage(ImgD,imglen){
   var image=new Image();
   var iwidth; 
       iwidth=imglen;  //定义允许图片宽度
   var iheight; 
       iheight=imglen;  //定义允许图片高度
   image.src=ImgD.src;
   if(image.width>0 && image.height>0){
    flag=true;
    if(image.width/image.height>= iwidth/iheight){
     if(image.width>iwidth){  
     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.height>iheight){  
     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;
     }
    }
}