var flag=false;  
function DrawImage(ImgD){  
 var image=new Image();  
 var iwidth = 320;  //定义允许图片宽度  
 var iheight = 320;  //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;  
  }  
 }  
}