Javascriptは画像のサイズを取得します.

<%= form_tag '/blogs/upphoto', :id => "upform", :multipart => true, :target => "showupimg", :onsubmit => "return uploadcheck();" %> 
<span style="margin-left:30px;"></span> 
<input class="imgfile" name="imgfile" type="file" size="40"/> 
<input class="upbutton" name="upload" type="submit" value="   " /> 
</form> 

//          form      
function uploadcheck(){ 
  //        
  var upform = document.getElementById('upform'); 
  var imgstring = document.getElementById('upform').imgfile.value; 
  if (imgstring == ''){  //      ？ 
   alert("        "); 
   return false; 
  } 
  imgtype = imgstring.substring(imgstring.lastIndexOf(".")+1, imgstring.length).toLowerCase();   
  alert(imgtype); 
  //      
  if (imgtype != "gif" && imgtype != "jpg" && imgtype != "jpeg" && imgtype != "png" && imgtype != "bmp"){   
   alert( "          ，   JPEG.JPG.GIF.PNG.BMP      ！ " )   
   return false ;   
  } 
  //         
  var img = new Image(); 
  var MAXSIZE = 1000; 
  alert(imgstring); 
  img.src = imgstring; 
  alert(img.fileSize); 
  if (img.fileSize > MAXSIZE*1024) { 
   alert( "       1M     " );   
   return false ;   
  } 
  var img_count = document.getElementById("showimgs").getElementsByTagName("img").length; 
  if (img_count >= 15) { 
   alert("       15    ，      ，     ，     ,   ！"); 
   return false; 
  } 
}   


img.fileSize              。