protected void btnpic_upload_Click(object sender, EventArgs e)
  { 
   #region 上傳文件
   Boolean fileOk = false;
   if (pic_upload.HasFile)//驗證是否包含文件
   {
    //取得文件的擴展名,并轉換成小寫
    string fileExtension = Path.GetExtension(pic_upload.FileName).ToLower();
    //驗證上傳文件是否圖片格式
    fileOk = IsImage(fileExtension);

    if (fileOk)
    {
     //對上傳文件的大小進行檢測，限定文件最大不超過8M
     if (pic_upload.PostedFile.ContentLength  8192000)
     {

      string filepath = "~/Admin/I_Institution/Images/";
      if (Directory.Exists(Server.MapPath(filepath)) == false)//如果不存在就創建file文件夾
      {
       Directory.CreateDirectory(Server.MapPath(filepath));
      }
      string virpath = filepath + CreatePasswordHash(pic_upload.FileName, 4) + fileExtension;//這是存到服務器上的虛擬路徑
      string mappath = Server.MapPath(virpath);//轉換成服務器上的物理路徑
      pic.Visible = true;

      pic_upload.PostedFile.SaveAs(mappath);//保存圖片
      //顯示圖片
      pic.ImageUrl = virpath;
      lbl_pic.Visible = true;
      //清空提示
      lbl_pic.Text = "上傳成功";
     }
     else
     {
      pic.Visible = false;
      lbl_pic.Visible = true;
      pic.ImageUrl = "";
      lbl_pic.Text = "文件大小超出8M！請重新選擇！";
     }
    }
    else
    {
     lbl_pic.Visible = false;
     pic.ImageUrl = "";
     lbl_pic.Text = "要上傳的文件類型不對！請重新選擇！";
    }
   }
   else
   {
    lbl_pic.Visible = false;
    pic.ImageUrl = "";
    lbl_pic.Text = "請選擇要上傳的圖片！";
   }
   #endregion
  }

  /// summary>
  /// 驗證是否指定的圖片格式
  /// /summary>
  /// param name="str">/param>
  /// returns>/returns>
  public bool IsImage(string str)
  {
   bool isimage = false;
   string thestr = str.ToLower();
   //限定只能上傳jpg和gif圖片
   string[] allowExtension = { ".jpg", ".gif", ".bmp", ".png" };
   //對上傳的文件的類型進行一個個匹對
   for (int i = 0; i  allowExtension.Length; i++)
   {
    if (thestr == allowExtension[i])
    {
     isimage = true;
     break;
    }
   }
   return isimage;
  }

  /// summary>
  /// 創建一個指定長度的隨機salt值
  /// /summary>
  public string CreateSalt(int saltLenght)
  {
   //生成一個加密的隨機數
   RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
   byte[] buff = new byte[saltLenght];
   rng.GetBytes(buff);
   //返回一個Base64隨機數的字符串
   return Convert.ToBase64String(buff);
  }

  /// summary>
  /// 返回加密后的字符串
  /// /summary>
  public string CreatePasswordHash(string pwd, int saltLenght)
  {
   string strSalt = CreateSalt(saltLenght);
   //把密碼和Salt連起來
   string saltAndPwd = String.Concat(pwd, strSalt);
   //對密碼進行哈希
   string hashenPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");
   //轉為小寫字符并截取前16個字符串
   hashenPwd = hashenPwd.ToLower().Substring(0, 16);
   //返回哈希后的值
   return hashenPwd;
  }

tr>
      td height="25" width="30%" align="right">
       機構圖標路徑 ：
      /td>
      td height="25" width="*" align="left">
       asp:Image ID="pic" runat="server" Width="200px" Visible="False" />br />
       asp:FileUpload ID="pic_upload" runat="server" />
       asp:Button ID="btnpic_upload" runat="server" Text="圖片開始上傳" OnClick="btnpic_upload_Click" />br />
       asp:Label ID="lbl_pic" runat="server" Text="" Visible="False">/asp:Label>
      /td>
     /tr>