1、按照你的要求,则在img tag 的onload事件中使用js处理重新设置大小即可。
2、不按照你的要求,则很多网站是给图片生成一个thumbNail图标,这样更快更方便。对于1,可参照:
<script   language="javascript">     
  var   flag=false;       
  function   DrawImage(ImgD){       
        var   image=new   Image();     
        image.src=ImgD.src;       
        if(image.width>0   &&   image.height>0){       
          flag=true;       
          if(image.width/image.height>=500/400){       
            if(image.width>500){           
            ImgD.width=500;       
            ImgD.height=(image.height*400)/image.width;       
            }else{       
            ImgD.width=image.width;           
            ImgD.height=image.height;       
            }       
            }       
          else{       
            if(image.height>400){           
            ImgD.height=400;       
            ImgD.width=(image.width*500)/image.height;                 
            }else{       
            ImgD.width=image.width;           
            ImgD.height=image.height;       
            }       
            }       
          }       
        }         
  </script> <IMG     src="<%=rs("pic")%>"   border=0     onload="javascript:DrawImage(this);"   >