圖片驗證碼控制元件

<img id="imgYZM" src="CheckCode.aspx"   onmouseup="RefreshCheckImage()" alt="點選重新獲取" />

點選再次獲取驗證碼

        function RefreshCheckImage() {
            var el = document.getElementById("imgYZM");
            el.src = el.src + '?'; //這個即為再次訪問，重新整理驗證碼
        }

CheckCode.aspx 頁面生成驗證碼

    /// <summary>
    /// 生成驗證碼，寫入Session["CheckCode"]
    /// </summary>
    public partial class CheckCode : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            this.CreateCheckCodeImage(RndNum());
        }

        private string RndNum()
        {
            int number;
            char code;
            string checkCode = String.Empty;

            Random random = new Random();

            for (int i = 0; i < 4; i++)
            {
                number = random.Next();
                if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('A' + (char)(number % 26));
                checkCode += code.ToString();
            }

            Session["CheckCode"] = checkCode;
            //Response.Cookies.Add(new HttpCookie("checkcode", checkCode));
            return checkCode;
        }

        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
            {
                //生成隨機生成器
                Random random = new Random();
                //清空圖片背景色
                g.Clear(Color.White);
                //畫圖片的背景噪音線
                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, (FontStyle.Bold | FontStyle.Italic));
                //System.Drawing.Drawing2D
                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);
                //畫圖片的前景噪音點
                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()));
                }
                //畫圖片的邊框線
                g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1);
                System.IO.MemoryStream ms = new System.IO.MemoryStream();
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
                Response.ClearContent();
                Response.ContentType = "image/Gif";
                Response.BinaryWrite(ms.ToArray());
            }
            finally
            {
                g.Dispose();
                image.Dispose();
            }
        }

    }