實現代碼

代碼如下:
/// <summary>
    /// 生成驗證碼圖片，保存session名稱VerificationCode
    /// </summary>
    public static void CreateVerificationCode()
    {
        int number;
        string checkCode = string.Empty;

        //隨機數種子
        Random randoms = new Random();

        for (int i = 0; i < 4; i++) //校驗碼長度為4
        {
            //隨機的整數
            number = randoms.Next();

            //字符從0-9,A-Z中隨機產生,對應的ASCII碼分別為
            //48-57,65-90
            number = number % 36;
            if (number < 10)
            {
                number += 48;
            }
            else
            {
                number += 55;
            }
            checkCode += ((char)number).ToString();
        }

        //在session中保存校驗碼
        System.Web.HttpContext.Current.Session["VerificationCode"] = checkCode;

        //若校驗碼為空，則直接返回
        if (checkCode == null || checkCode.Trim() == String.Empty)
        {
            return;
        }
        //根據校驗碼的長度確定輸出圖片的長度
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(55, 20);//(int)Math.Ceiling(Convert.ToDouble(checkCode.Length * 15))
        //創建Graphics對象
        Graphics g = Graphics.FromImage(image);
        try