验证码

/// <summary>
/// 验证码类
/// </summary>
public static class StringCAPTCHA
{
    /// <summary>
    /// create a random key
    /// </summary>
    static readonly Random Random = new Random(~unchecked((int)DateTime.Now.Ticks));
    static readonly char[] NumberList = { '1', '2', '3', '4', '5', '6', '7', '8', '9' };
    static readonly char[] CharList = { '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' };
    static readonly char[] MixedList = { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z' }; //remove I & O

    #region 生成随机数字
    /// <summary>
    /// 生成随机数字
    /// </summary>
    /// <param name="Length">生成长度</param>
    public static string Number(int Length)
    {
        return Create(Length, false, NumberList);
    }

    /// <summary>
    /// 生成随机数字
    /// </summary>
    /// <param name="Length">生成长度</param>
    /// <param name="Sleep">是否要在生成前将当前线程阻止以避免重复</param>
    public static string Number(int Length, bool Sleep)
    {
        return Create(Length, Sleep, NumberList);
    }
    #endregion

    #region 生成随机字母与数字
    /// <summary>
    /// 生成随机字母与数字
    /// </summary>
    /// <param name="Length">生成长度</param>
    public static string Mixed(int Length)
    {
        return Create(Length, false, MixedList);
    }

    /// <summary>
    /// 生成随机字母与数字
    /// </summary>
    /// <param name="Length">生成长度</param>
    /// <param name="Sleep">是否要在生成前将当前线程阻止以避免重复</param>
    public static string Mixed(int Length, bool Sleep)
    {
        return Create(Length, Sleep, MixedList);
    }
    #endregion

    #region 生成随机纯字母随机数
    /// <summary>
    /// 生成随机纯字母随机数
    /// </summary>
    /// <param name="Length">生成长度</param>
    public static string Char(int Length)
    {
        return Create(Length, false, CharList);
    }

    /// <summary>
    /// 生成随机纯字母随机数
    /// </summary>
    /// <param name="Length">生成长度</param>
    /// <param name="Sleep">是否要在生成前将当前线程阻止以避免重复</param>
    public static string Char(int Length, bool Sleep)
    {
        return Create(Length, Sleep, CharList);
    }
    #endregion

    /// <summary>
    /// Create the CAPTCHA specified Length, Sleep and List.
    /// </summary>
    /// <returns>The create.</returns>
    /// <param name="Length">Length.</param>
    /// <param name="Sleep">If set to <c>true</c> sleep.</param>
    /// <param name="List">List create CAPTCHA based on</param>
    private static string Create(int Length, bool Sleep, char[] List)
    {
        if (Sleep) Thread.Sleep(3);
        char[] Pattern = List;
        string result = string.Empty;
        int n = Pattern.Length;

        for (int i = 0; i < Length; i++)
        {
            int rnd = Random.Next(0, n);
            result += Pattern[rnd];
        }
        return result;
    }



}

/// <summary>
/// 验证图片类
/// </summary>
public class PictureCAPTCHA
{
    #region 私有字段
    private string text { get; set; }
    private Bitmap image { get; set; }
    private int LetterCount { set; get; }  //验证码位数
    private int Type { set; get; }
    private int letterWidth = 16;  //单个字体的宽度范围
    private int letterHeight = 20; //单个字体的高度范围
    private static Random Random = new Random(~unchecked((int)DateTime.Now.Ticks));
    private Font[] fonts =
    {
       new Font(new FontFamily("Times New Roman"),10 +Random.Next(1),FontStyle.Regular),
       new Font(new FontFamily("Georgia"), 10 + Random.Next(1),FontStyle.Regular),
       new Font(new FontFamily("Arial"), 10 + Random.Next(1),FontStyle.Regular),
       new Font(new FontFamily("Comic Sans MS"), 10 + Random.Next(1),FontStyle.Regular)
    };
    #endregion

    #region 公有属性
    /// <summary>
    /// 验证码
    /// </summary>
    public string Text
    {
        get { return this.text; }
    }

    /// <summary>
    /// 验证码图片
    /// </summary>
    public Bitmap Image
    {
        get { return this.image; }
    }
    #endregion

    #region constructor
    /// <summary>
    /// Initializes a new instance of the <see cref="T:DotNet.Utilities.PictureCAPTCHA"/> class. default length is 4 with number list 
    /// </summary>
    public PictureCAPTCHA()
    {
        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";
        LetterCount = 4;
        Type = 0;
        InitText();
        CreateImage();
    }
    /// <summary>
    /// Initializes a new instance of the <see cref="T:DotNet.Utilities.PictureCAPTCHA"/> class with number list;
    /// </summary>
    /// <param name="Length">Length.</param>
    public PictureCAPTCHA(int Length)
    {
        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";
        LetterCount = Length;
        text = StringCAPTCHA.Number(LetterCount);
        CreateImage();
    }
    /// <summary>
    /// Initializes a new instance of the <see cref="T:DotNet.Utilities.PictureCAPTCHA"/> class.
    /// </summary>
    /// <param name="Length">Length.</param>
    /// <param name="type">Type 0 number , 1 char , 2 mixed.</param>
    public PictureCAPTCHA(int Length, int type)
    {
        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";
        LetterCount = Length;
        Type = type;
        InitText();
        CreateImage();
    }

    #endregion

    #region Public function

    public void Redraw(bool NewCAPTCHA)
    {
        if (NewCAPTCHA)
        {
            InitText();
        }
        CreateImage();
    }

    #endregion


    #region private funcation

    private void InitText()
    {
        switch (Type)
        {
            case 0: text = StringCAPTCHA.Number(LetterCount); break;
            case 1: text = StringCAPTCHA.Char(LetterCount); break;
            case 2: text = StringCAPTCHA.Mixed(LetterCount); break;
            default:

                break;
        }
    }

    /// <summary>
    /// 绘制验证码
    /// </summary>
    private void CreateImage()
    {
        int ImageWidth = this.Text.Length * letterWidth;
        Bitmap Img = new Bitmap(ImageWidth, letterHeight);
        Graphics g = Graphics.FromImage(Img);
        g.Clear(Color.White);
        for (int i = 0; i < 2; i++)
        {
            int x1 = Random.Next(Img.Width - 1);
            int x2 = Random.Next(Img.Width - 1);
            int y1 = Random.Next(Img.Height - 1);
            int y2 = Random.Next(Img.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 += Random.Next(12, 16);
            _y = Random.Next(-2, 2);
            string str_char = this.Text.Substring(int_index, 1);
            str_char = Random.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[Random.Next(fonts.Length - 1)], newBrush, thePos);
        }
        for (int i = 0; i < 10; i++)
        {
            int x = Random.Next(Img.Width - 1);
            int y = Random.Next(Img.Height - 1);
            Img.SetPixel(x, y, Color.FromArgb(Random.Next(0, 255), Random.Next(0, 255), Random.Next(0, 255)));
        }
        Img = TwistImage(Img, true, Random.Next(1, 3), Random.Next(4, 6));
        g.DrawRectangle(new Pen(Color.LightGray, 1), 0, 0, ImageWidth - 1, (letterHeight - 1));
        image = Img;
    }


    /// <summary>
    /// 字体随机颜色
    /// </summary>
    private Color GetRandomColor()
    {
        Random RandomNum_First = new Random((int)DateTime.Now.Ticks);
        Thread.Sleep(RandomNum_First.Next(50));
        Random RandomNum_Sencond = new Random((int)DateTime.Now.Ticks);
        int int_Red = RandomNum_First.Next(180);
        int int_Green = RandomNum_Sencond.Next(180);
        int int_Blue = (int_Red + int_Green > 300) ? 0 : 400 - int_Red - int_Green;
        int_Blue = (int_Blue > 255) ? 255 : int_Blue;
        return Color.FromArgb(int_Red, int_Green, int_Blue);
    }

    /// <summary>
    /// 正弦曲线Wave扭曲图片
    /// </summary>
    /// <param name="srcBmp">图片路径</param>
    /// <param name="bXDir">如果扭曲则选择为True</param>
    /// <param name="dMultValue">波形的幅度倍数，越大扭曲的程度越高,一般为3</param>
    /// <param name="dPhase">波形的起始相位,取值区间[0-2*PI)</param>
    private Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
    {
        double PI = 6.283185307179586476925286766559;
        Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
        Graphics graph = Graphics.FromImage(destBmp);
        graph.FillRectangle(new SolidBrush(Color.White), 0, 0, destBmp.Width, destBmp.Height);
        graph.Dispose();
        double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
        for (int i = 0; i < destBmp.Width; i++)
        {
            for (int j = 0; j < destBmp.Height; j++)
            {
                double dx = 0;
                dx = bXDir ? (PI * (double)j) / dBaseAxisLen : (PI * (double)i) / dBaseAxisLen;
                dx += dPhase;
                double dy = Math.Sin(dx);
                int nOldX = 0, nOldY = 0;
                nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
                nOldY = bXDir ? j : j + (int)(dy * dMultValue);

                Color color = srcBmp.GetPixel(i, j);
                if (nOldX >= 0 && nOldX < destBmp.Width
                 && nOldY >= 0 && nOldY < destBmp.Height)
                {
                    destBmp.SetPixel(nOldX, nOldY, color);
                }
            }
        }
        srcBmp.Dispose();
        return destBmp;
    }
    #endregion
}

控制器代码

    public ActionResult GetCaptcha()
    {
        PictureCAPTCHA cpa = new PictureCAPTCHA(4, 2);
        using (MemoryStream stream = new MemoryStream())
        {
            cpa.Image.Save(stream, ImageFormat.Jpeg);
            byte[] data = new byte[stream.Length];
            stream.Seek(0, SeekOrigin.Begin);
            stream.Read(data, 0, Convert.ToInt32(stream.Length));

            SessionHelper.RemoveSession("captcha");
            SessionHelper.SetSession("captcha", cpa.Text);

            return File(data, "image / Jpeg");
        }
    }

HTML

<img class="capimg" src="/Home/GetCaptcha" />