验证上传文件类型的问题

$upload_img=$_FILES['img']['tmp_name'];
$img=$_FILES['img']['name'];
if (strlen($img)!=0)
{   
  if (eregi("\.(".$uploadtype.")$",$img))
   {
   if (eregi("\.(gif|jpg|jpeg|png|bmp)$",$img))
         {
         if (eregi("\.(jpeg)$",$img))
        {
    $strcut1=substr($img,-5);
    }
    else
    {
    $strcut1=substr($img,-4);
    }
         $type="gif";
 //list($width, $height, $type, $attr)=GetImageSize($upload_img);
 }
 elseif (eregi("\.(swf)$",$img))
 {
 $strcut1=substr($img,-4);
 $type="swf";
 }
 elseif (eregi("\.(zip|rar)$",$img))
 {
 $strcut1=substr($img,-4);
 $type="rar";
 }
 elseif (eregi("\.(mid|ram|rm|mpg|wmv)$",$img))
 {
     if (eregi("\.(rm)$",$img))
    {
        $strcut1=substr($img,-3);
}
else
{
        $strcut1=substr($img,-4);
}
 $type="mid";
 }
 elseif (eregi("\.(mp3|wma)$",$img))
 {
 $strcut1=substr($img,-4);
 $type="mp3";
 }
     else
     {
 $strcut1=substr($img,-4);
 $type="unt";//未知类型
     }
   $upload_img_name=md5($img).md5(time()).md5($_COOKIE['usernamecookies'].$_COOKIE['useridcookies']).$strcut1;
   }
   else
   {
   echo "<script language=javascript>alert('您选择的文件不在允许的上传类型中，请重新选择文件');history.go(-1);</script>";
   exit;
   }
}
else
{
$upload_img_name=0;
$type=0;
}
if($upload_img)
{
$doc=date('Y-m-d',time()+28800);
    $store_dir = $path1."/";
if (!file_exists($store_dir)) 
      {
      mkdir($store_dir,0777);
  }
    $accept_overwrite = 1;
$filesize=filesize($upload_img)/1024/1024;
$abc=ini_get('upload_max_filesize');
  if ($uploadmax<=$abc)
    {
         if ($filesize>$uploadmax)
     {
          echo "对不起，您的系统不允许上传超过 ".$uploadmax."M 的文件！";
          exit;
         }
}
else
{
echo "您的服务器不允许上传超过".$abc."的文件！";
exit;
}
  if (file_exists($store_dir . $upload_img_name) && !$accept_overwrite) 
     {
          echo  "存在相同文件名的文件！";
          exit;
          }
  if (!move_uploaded_file($upload_img,$store_dir.$upload_img_name))
     {
         echo "复制文件失败";
         exit;
         }
}