驗證碼是現在管理系統常用的一種保護用戶帳戶信息的一種功能。

驗證碼可以有效防止某個黑客對某一個特定注冊用戶用特定程序暴力破解方式進行不斷的登錄嘗試，雖然這可能是我們登錄麻煩一點，但是對用戶的密碼安全來說這個功能還是很有必要，也很重要。但在這里我還是要提醒大家要保護好自己的密碼同時盡量使自己的密碼復雜度高一點，免得你的賬號被人盜用后給自己帶來不必要的麻煩。

現在使用的驗證碼類是蘇飛論壇的蘇飛所寫，本人只是學習和使用而已，驗證碼類如下所示：

/// <summary>/// 類說明：YZMHelper/// 編 碼 人：蘇飛/// 聯系方式：361983679  /// 更新網站：http://www.sufeinet.com/thread-655-1-1.html/// </summary>using System;using System.Web;using System.Drawing;using System.Security.Cryptography;namespace DotNet.Utilities{    /// <summary>    /// 驗證碼類    /// </summary>    public class Rand    {        #region 生成隨機數字        /// <summary>        /// 生成隨機數字        /// </summary>        /// <param name="length">生成長度</param>        public static string Number(int Length)        {            return Number(Length, false);        }        /// <summary>        /// 生成隨機數字        /// </summary>        /// <param name="Length">生成長度</param>        /// <param name="Sleep">是否要在生成前將當前線程阻止以避免重復</param>        public static string Number(int Length, bool Sleep)        {            if (Sleep) System.Threading.Thread.Sleep(3);            string result = "";            System.Random random = new Random();            for (int i = 0; i < Length; i++)            {                result += random.Next(10).ToString();            }            return result;        }        #endregion        #region 生成隨機字母與數字        /// <summary>        /// 生成隨機字母與數字        /// </summary>        /// <param name="IntStr">生成長度</param>        public static string Str(int Length)        {            return Str(Length, false);        }        /// <summary>        /// 生成隨機字母與數字        /// </summary>        /// <param name="Length">生成長度</param>        /// <param name="Sleep">是否要在生成前將當前線程阻止以避免重復</param>        public static string Str(int Length, bool Sleep)        {            if (Sleep) System.Threading.Thread.Sleep(3);            char[] Pattern = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };            string result = "";            int n = Pattern.Length;            System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));            for (int i = 0; i < Length; i++)            {                int rnd = random.Next(0, n);                result += Pattern[rnd];            }            return result;        }        #endregion        #region 生成隨機純字母隨機數        /// <summary>        /// 生成隨機純字母隨機數        /// </summary>        /// <param name="IntStr">生成長度</param>        public static string Str_char(int Length)        {            return Str_char(Length, false);        }        /// <summary>        /// 生成隨機純字母隨機數        /// </summary>        /// <param name="Length">生成長度</param>        /// <param name="Sleep">是否要在生成前將當前線程阻止以避免重復</param>        public static string Str_char(int Length, bool Sleep)        {            if (Sleep) System.Threading.Thread.Sleep(3);            char[] Pattern = new char[] { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' };            string result = "";            int n = Pattern.Length;            System.Random random = new Random(~unchecked((int)DateTime.Now.Ticks));            for (int i = 0; i < Length; i++)            {                int rnd = random.Next(0, n);                result += Pattern[rnd];            }            return result;        }        #endregion    }    /// <summary>    /// 驗證圖片類    /// </summary>    public class YZMHelper    {        #region 私有字段        PRivate string text;        private Bitmap image;        private int letterCount = 4;   //驗證碼位數        private int letterWidth = 16;  //單個字體的寬度范圍        private int letterHeight = 20; //單個字體的高度范圍        private static byte[] randb = new byte[4];        private static RNGCryptoServiceProvider rand = new RNGCryptoServiceProvider();        private Font[] fonts =     {       new Font(new FontFamily("Times New Roman"),10 +Next(1),System.Drawing.FontStyle.Regular),       new Font(new FontFamily("Georgia"), 10 + Next(1),System.Drawing.FontStyle.Regular),       new Font(new FontFamily("Arial"), 10 + Next(1),System.Drawing.FontStyle.Regular),       new Font(new FontFamily("Comic Sans MS"), 10 + Next(1),System.Drawing.FontStyle.Regular)    };        #endregion        #region 公有屬性        /// <summary>        /// 驗證碼        /// </summary>        public string Text        {            get { return this.text; }        }        /// <summary>        /// 驗證碼圖片        /// </summary>        public Bitmap Image        {            get { return this.image; }        }        #endregion        #region 構造函數        public YZMHelper()        {            HttpContext.Current.Response.Expires = 0;            HttpContext.Current.Response.Buffer = true;            HttpContext.Current.Response.ExpiresAbsolute = DateTime.Now.AddSeconds(-1);            HttpContext.Current.Response.AddHeader("pragma", "no-cache");            HttpContext.Current.Response.CacheControl = "no-cache";            this.text = Rand.Number(4);            CreateImage();        }        #endregion        #region 私有方法        /// <summary>        /// 獲得下一個隨機數        /// </summary>        /// <param name="max">最大值</param>        private static int Next(int max)        {            rand.GetBytes(randb);            int value = BitConverter.ToInt32(randb, 0);            value = value % (max + 1);            if (value < 0) value = -value;            return value;        }        /// <summary>        /// 獲得下一個隨機數        /// </summary>        /// <param name="min">最小值</param>        /// <param name="max">最大值</param>        private static int Next(int min, int max)        {            int value = Next(max - min) + min;            return value;        }        #endregion        #region 公共方法        /// <summary>        /// 繪制驗證碼        /// </summary>        public void CreateImage()        {            int int_ImageWidth = this.text.Length * letterWidth;            Bitmap image = new Bitmap(int_ImageWidth, letterHeight);            Graphics g = Graphics.FromImage(image);            g.Clear(Color.White);            for (int i = 0; i < 2; i++)            {                int x1 = Next(image.Width - 1);                int x2 = Next(image.Width - 1);                int y1 = Next(image.Height - 1);                int y2 = Next(image.Height - 1);                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);            }            int _x = -12, _y = 0;            for (int int_index = 0; int_index < this.text.Length; int_index++)            {                _x += Next(12, 16);                _y = Next(-2, 2);                string str_char = this.text.Substring(int_index, 1);                str_char = Next(1) == 1 ? str_char.ToLower() : str_char.ToUpper();                Brush newBrush = new SolidBrush(GetRandomColor());                Point thePos = new Point(_x, _y);                g.DrawString(str_char, fonts[Next(fonts.Length - 1)], newBrush, thePos);            }            for (int i = 0; i < 10; i++)            {                int x = Next(image.Width - 1);                int y = Next(image.Height - 1);                image.SetPixel(x, y, Color.FromArgb(Next(0, 255), Next(0, 255), Next(0, 255)));            }            image = TwistImage(image, true, Next(1, 3), Next(4, 6));            g.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, int_ImageWidth - 1, (letterHeight - 1));            this.image = image;        }        /// <summary>        /// 字體隨機顏色        /// </summary>        public Color GetRandomColor()        {            Random RandomNum_First = new Random((int)DateTime.Now.Ticks);            System.Threading.Thread.Sleep(RandomNum_First.Next(50));            Random RandomNum_Se