ASP.NET 验证码创建及刷新

验证码页面后台Code.aspx.cs代码：（已经将验证码存于session中session["code"]，可在调用页面直接读取session）
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing; //添加引用
public partial class Code : System.Web.UI.Page
{
static string[] FontItems = new string[] { "Arial",
"Helvetica",
"Geneva",
"sans-serif",
"Verdana"
};
static Brush[] BrushItems = new Brush[] { Brushes.OliveDrab,
Brushes.ForestGreen,
Brushes.DarkCyan,
Brushes.LightSlateGray,
Brushes.RoyalBlue,
Brushes.SlateBlue,
Brushes.DarkViolet,
Brushes.MediumVioletRed,
Brushes.IndianRed,
Brushes.Firebrick,
Brushes.Chocolate,
Brushes.Peru,
Brushes.Goldenrod
};
static string[] BrushName = new string[] { "OliveDrab",
"ForestGreen",
"DarkCyan",