ASPX页面添加验证码

        protected void Page_Load(object sender, EventArgs e)
        {
            if(!IsPostBack){
                CreateCheckCodeImage(GenerateCheckCode());//调用下面两个方法;
            }
        }
        /// <summary>
        /// 生成验证码的随机数
        /// </summary>
        /// <returns>返回五位随机数</returns>
        private string GenerateCheckCode()
        {
            int number;
            char code;
            string checkCode = String.Empty;

            Random random = new Random();

            for (int i = 0; i < 5; i++)//可以任意设定生成验证码的位数
            {
                number = random.Next();

                if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('A' + (char)(number % 26));

                checkCode += code.ToString();
            }

            Response.Cookies.Add(new HttpCookie("CheckCode", checkCode));//写入COOKIS
            Session["CheckCode"] = checkCode;  //写入Session，可以任意选一下
            return checkCode;
        }


        /// <summary>
        /// 生成验证码图片
        /// </summary>
        /// <param name="checkCode"></param>
        private void CreateCheckCodeImage(string checkCode)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;

            Bitmap image = new Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
            Graphics g = Graphics.FromImage(image);

            try
            {
                //生成随机生成器
                Random random = new Random();

                //清空图片背景色
                g.Clear(Color.White);

                //画图片的背景噪音线
                for (int i = 0; i < 25; i++)
                {
                    int x1 = random.Next(image.Width);
                    int x2 = random.Next(image.Width);
                    int y1 = random.Next(image.Height);
                    int y2 = random.Next(image.Height);

                    g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
                }

                Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
                LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
                g.DrawString(checkCode, font, brush, 2, 2);

                //画图片的前景噪音点
                for (int i = 0; i < 100; i++)
                {
                    int x = random.Next(image.Width);
                    int y = random.Next(image.Height);

                    image.SetPixel(x, y, Color.FromArgb(random.Next()));
                }

                //画图片的边框线
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

                MemoryStream ms = new MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {//释放对象资源
                g.Dispose();
                image.Dispose();
            }
        }

 

 

 

前台页面：  <asp:Image ID="Image1" runat="server"  src="ImgPng.aspx" style="cursor:pointer" onclick="this.src=this.src+'?'" align="middle"  alt="看不清楚，点击换一张！"   />

判断用session：  if (Session["CheckCode"].ToString().Trim().Equals(TextBox3.Text.Trim().ToUpper()))