protected void btnpic_upload_Click(object sender, EventArgs e)
 { 
  #region 上传文件
  Boolean fileOk = false;
  if (pic_upload.HasFile)//验证是否包含文件
  {
  //取得文件的扩展名,并转换成小写
  string fileExtension = Path.GetExtension(pic_upload.FileName).ToLower();
  //验证上传文件是否图片格式
  fileOk = IsImage(fileExtension);

  if (fileOk)
  {
   //对上传文件的大小进行检测，限定文件最大不超过8M
   if (pic_upload.PostedFile.ContentLength < 8192000)
   {

   string filepath = "~/Admin/I_Institution/Images/";
   if (Directory.Exists(Server.MapPath(filepath)) == false)//如果不存在就创建file文件夹
   {
    Directory.CreateDirectory(Server.MapPath(filepath));
   }
   string virpath = filepath + CreatePasswordHash(pic_upload.FileName, 4) + fileExtension;//这是存到服务器上的虚拟路径
   string mappath = Server.MapPath(virpath);//转换成服务器上的物理路径
   pic.Visible = true;

   pic_upload.PostedFile.SaveAs(mappath);//保存图片
   //显示图片
   pic.ImageUrl = virpath;
   lbl_pic.Visible = true;
   //清空提示
   lbl_pic.Text = "上传成功";
   }
   else
   {
   pic.Visible = false;
   lbl_pic.Visible = true;
   pic.ImageUrl = "";
   lbl_pic.Text = "文件大小超出8M！请重新选择！";
   }
  }
  else
  {
   lbl_pic.Visible = false;
   pic.ImageUrl = "";
   lbl_pic.Text = "要上传的文件类型不对！请重新选择！";
  }
  }
  else
  {
  lbl_pic.Visible = false;
  pic.ImageUrl = "";
  lbl_pic.Text = "请选择要上传的图片！";
  }
  #endregion
 }

 /// <summary>
 /// 验证是否指定的图片格式
 /// </summary>
 /// <param name="str"></param>
 /// <returns></returns>
 public bool IsImage(string str)
 {
  bool isimage = false;
  string thestr = str.ToLower();
  //限定只能上传jpg和gif图片
  string[] allowExtension = { ".jpg", ".gif", ".bmp", ".png" };
  //对上传的文件的类型进行一个个匹对
  for (int i = 0; i < allowExtension.Length; i++)
  {
  if (thestr == allowExtension[i])
  {
   isimage = true;
   break;
  }
  }
  return isimage;
 }

 /// <summary>
 /// 创建一个指定长度的随机salt值
 /// </summary>
 public string CreateSalt(int saltLenght)
 {
  //生成一个加密的随机数
  RNGCryptoServiceProvider rng = new RNGCryptoServiceProvider();
  byte[] buff = new byte[saltLenght];
  rng.GetBytes(buff);
  //返回一个Base64随机数的字符串
  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);
  //把密码和Salt连起来
  string saltAndPwd = String.Concat(pwd, strSalt);
  //对密码进行哈希
  string hashenPwd = FormsAuthentication.HashPasswordForStoringInConfigFile(saltAndPwd, "sha1");
  //转为小写字符并截取前16个字符串
  hashenPwd = hashenPwd.ToLower().Substring(0, 16);
  //返回哈希后的值
  return hashenPwd;
 }

tr>
   <td height="25" width="30%" align="right">
    机构图标路径 ：
   </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="图片开始上传" OnClick="btnpic_upload_Click" /><br />
    <asp:Label ID="lbl_pic" runat="server" Text="" Visible="False"></asp:Label>
   </td>
   </tr>