html xmlns="http://www.w3.org/1999/xhtml">
head runat="server">
  title>驗證碼/title>
  script type="text/javascript">
    //換一張
    function change() {
      var img = document.getElementById("ValidateCode");
      img.src = img.src + '?';
    }
  /script>
/head>
body>
  form id="form1" runat="server">
  div>
    table>
      tr>
        th>
          驗證碼
        /th>
        td>
          asp:TextBox runat="server" ID="tbCheckCode" CssClass="Small" MaxLength="4">/asp:TextBox>
        /td>
        td>
          img src="VerifyCode.aspx" id="ValidateCode" alt="換一張" onclick="javascript:change()" />
        /td>
        td>
          a id="ChangeCode" href="#" onclick="javascript:change()">換一張/a>
        /td>
      /tr>
      tr>
        td>
          asp:Button runat="server" ID="LoginSubmit" OnClick="LoginSubmits" Text="登錄" />
        /td>
      /tr>
    /table>
  /div>
  /form>
/body>
/html>

    /// summary>
    /// 登錄
    /// /summary>
    /// param name="sender">/param>
    protected void LoginSubmits(object sender, EventArgs e)
    {
      CheckLogin();
    }

    #region 私有方法
    #region
    public static Boolean IsNotNull(Object str)
    {
      return !IsNull(str);
    }
    public static Boolean IsNull(Object str)
    {
      return str == null;
    }
    public static void Show(System.Web.UI.Page page, string msg)
    {
      page.ClientScript.RegisterStartupScript(page.GetType(), "message",
        "script language='javascript' defer>alert('" + msg.ToString() + "');/script>");
    }
    #endregion

    private void CheckLogin()
    {
      if (tbCheckCode.Text.Trim() == "")
      {
        Show(this, "驗證碼不能為空!");
        return;
      }
      else
      {
        if (IsNotNull(Session["ValidateCheckCode"]))
        {
          if (tbCheckCode.Text.Trim() != Session["ValidateCheckCode"].ToString())
          {
            Show(this, "驗證碼填寫不正確!");
            tbCheckCode.Text = "";
            return;
          }
        }
        else
        {
          Show(this, "請刷新驗證碼！");
          return;
        }
      }
    }
    #endregion
  }
}

using System;
using System.Drawing;
using System.Text;
using System.Web;

namespace Web.TEXT
{
  public partial class VerifyCode : System.Web.UI.Page
  {
    public Encoding GB = Encoding.GetEncoding("GB2312");

    protected void Page_Load(object sender, EventArgs e)
    {
      VerifyCode v = new VerifyCode();

      v.Length = this.length;
      v.FontSize = this.fontSize;
      v.Chaos = this.chaos;
      v.BackgroundColor = this.backgroundColor;
      v.ChaosColor = this.chaosColor;
      v.CodeSerial = this.codeSerial;
      v.Colors = this.colors;
      v.Fonts = this.fonts;
      v.Padding = this.padding;
      string code = v.CreateVerifyCode(); //取隨機碼
      v.CreateImageOnPage(code, this.Context); // 輸出圖片
      Response.Cookies.Add(new HttpCookie("CheckCode", code.ToUpper())); // 使用Cookies取驗證碼的值

      System.Web.HttpContext.Current.Session["ValidateCheckCode"] = code;
      //return checkCode;
    }

    #region 驗證碼長度(默認4個驗證碼的長度)

    private int length = 4; 

    public int Length
    {
      get { return length; }
      set { length = value; }
    }

    #endregion

    #region 驗證碼字體大小(為了顯示扭曲效果，默認40像素，可以自行修改)

    private int fontSize = 12;

    public int FontSize
    {
      get { return fontSize; }
      set { fontSize = value; }
    }

    #endregion

    #region 邊框補(默認1像素)

    private int padding = 1;

    public int Padding
    {
      get { return padding; }
      set { padding = value; }
    }

    #endregion

    #region 是否輸出燥點(默認不輸出)

    private bool chaos = true;

    public bool Chaos
    {
      get { return chaos; }
      set { chaos = value; }
    }

    #endregion

    #region 輸出燥點的顏色(默認灰色)

    private Color chaosColor = Color.LightGray;

    public Color ChaosColor
    {
      get { return chaosColor; }
      set { chaosColor = value; }
    }

    #endregion

    #region 自定義背景色(默認白色)

    private Color backgroundColor = Color.White;

    public Color BackgroundColor
    {
      get { return backgroundColor; }
      set { backgroundColor = value; }
    }

    #endregion

    #region 自定義隨機顏色數組

    private Color[] colors =
    {
      Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown,
      Color.DarkCyan, Color.Purple
    };

    public Color[] Colors
    {
      get { return colors; }
      set { colors = value; }
    }

    #endregion

    #region 自定義字體數組

    private string[] fonts = {"Arial", "Georgia"};

    public string[] Fonts
    {
      get { return fonts; }
      set { fonts = value; }
    }

    #endregion

    #region 自定義隨機碼字符串序列(使用逗號分隔)

    private string codeSerial = "0,1,2,3,4,5,6,7,8,9";
    // string codeSerial = "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,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 codeSerial = "殃,央,鴦,秧,楊,揚,佯,瘍,羊,洋,陽,氧,仰,癢,養,樣,漾,邀,腰,妖,瑤,搖,堯,遙,窯,謠,姚,咬,舀,藥,要,耀,椰,噎,耶,爺,野,冶,也,頁,掖,業,葉,曳,腋,夜,液,一,壹,醫,揖,銥,依,伊,衣,頤,夷,遺,移,儀,胰,疑,沂,宜,姨,彝,椅,蟻,倚,已,乙,矣,以,藝,抑,易,邑,屹,億,役,臆,逸,肄,疫,亦,裔,意,毅,憶,義,益,溢,詣,議,誼,譯,異,翼,翌,繹,茵,蔭,因,殷,音,陰,姻,吟,銀,淫,寅,飲,尹,引,隱,印,英,櫻,嬰,鷹,應,纓,瑩,螢,營,熒,蠅,迎,贏,盈,影,穎,硬,映,喲,擁,傭,臃,癰,庸,雍,踴,蛹,詠,泳,涌,永,恿,勇,用,幽,優,悠,憂,尤,由,郵,鈾,猶,油,游,酉,有,友,右,佑,釉,誘,又,幼,迂,淤,于,盂,榆,虞,愚,輿,余,俞,逾,魚,愉,渝,漁,隅,予,娛,雨,與,嶼,禹,株,蛛,朱,豬,諸,誅,逐,竹,燭,煮,拄,矚,囑,主,著,柱,助,蛀,貯,鑄,筑,住,注,祝,駐,抓,爪,拽,專,磚,轉,撰,賺,篆,樁,莊,裝,妝,撞,壯,狀,椎,錐,追,贅,墜,綴,諄,準,捉,拙,卓,桌,琢,茁,酌,啄,著,灼,濁,茲,咨,資,姿,滋,淄,孜,紫,仔,籽,滓,子,自,漬,字,鬃,棕,蹤,宗,綜,總,縱,鄒,走,奏,揍,租,足,卒,族,祖,詛,阻,組,鉆,纂,嘴,醉,最,罪,尊,遵,昨,左,佐,柞,做,作,坐,座";
    public string CodeSerial
    {
      get { return codeSerial; }
      set { codeSerial = value; }
    }

    #endregion

    //產生波形濾鏡效果

    #region 產生波形濾鏡效果

    private const double PI = 3.1415926535897932384626433832795;
    private const double PI2 = 6.283185307179586476925286766559;

    /**/

    /// summary>
    /// 正弦曲線Wave扭曲圖片（Edit By 51aspx.com）
    /// /summary>
    /// param name="srcBmp">圖片路徑/param>
    /// param name="bXDir">如果扭曲則選擇為True/param>
    /// param name="nMultValue">波形的幅度倍數，越大扭曲的程度越高，一般為3/param>
    /// param name="dPhase">波形的起始相位，取值區間[0-2*PI)/param>
    /// returns>/returns>
    public System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
    {
      System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);

      // 將位圖背景填充為白色
      System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp);
      graph.FillRectangle(new SolidBrush(System.Drawing.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 ? (PI2*(double) j)/dBaseAxisLen : (PI2*(double) i)/dBaseAxisLen;
          dx += dPhase;
          double dy = Math.Sin(dx);

          // 取得當前點的顏色
          int nOldX = 0, nOldY = 0;
          nOldX = bXDir ? i + (int) (dy*dMultValue) : i;
          nOldY = bXDir ? j : j + (int) (dy*dMultValue);

          System.Drawing.Color color = srcBmp.GetPixel(i, j);
          if (nOldX >= 0  nOldX  destBmp.Width
             nOldY >= 0  nOldY  destBmp.Height)
          {
            destBmp.SetPixel(nOldX, nOldY, color);
          }
        }
      }

      return destBmp;
    }



    #endregion

    #region 生成校驗碼圖片

    public Bitmap CreateImageCode(string code)
    {
      int fSize = FontSize;
      int fWidth = fSize + Padding;

      int imageWidth = (int) (code.Length*fWidth) + 4 + Padding*2;
      int imageHeight = fSize*2 + Padding;

      System.Drawing.Bitmap image = new System.Drawing.Bitmap(imageWidth, imageHeight);

      Graphics g = Graphics.FromImage(image);

      g.Clear(BackgroundColor);

      Random rand = new Random();

      //給背景添加隨機生成的燥點
      if (this.Chaos)
      {

        Pen pen = new Pen(ChaosColor, 0);
        int c = Length*10;

        for (int i = 0; i  c; i++)
        {
          int x = rand.Next(image.Width);
          int y = rand.Next(image.Height);

          g.DrawRectangle(pen, x, y, 1, 1);
        }
      }

      int left = 0, top = 0, top1 = 1, top2 = 1;

      int n1 = (imageHeight - FontSize - Padding*2);
      int n2 = n1/4;
      top1 = n2;
      top2 = n2*2;

      Font f;
      Brush b;

      int cindex, findex;

      #region 隨機字體和顏色的驗證碼字符

      for (int i = 0; i  code.Length; i++)
      {
        cindex = rand.Next(Colors.Length - 1);
        findex = rand.Next(Fonts.Length - 1);

        f = new System.Drawing.Font(Fonts[findex], fSize, System.Drawing.FontStyle.Bold);
        b = new System.Drawing.SolidBrush(Colors[cindex]);

        if (i%2 == 1)
        {
          top = top2;
        }
        else
        {
          top = top1;
        }

        left = i*fWidth;

        g.DrawString(code.Substring(i, 1), f, b, left, top);
      }

      //畫一個邊框 邊框顏色為Color.Gainsboro
      g.DrawRectangle(new Pen(Color.Gainsboro, 0), 0, 0, image.Width - 1, image.Height - 1);
      g.Dispose();

      //產生波形
      //image = TwistImage(image, true, 8, 4);

      return image;
    }

    #endregion

    //將創建好的圖片輸出到頁面
    public void CreateImageOnPage(string code, HttpContext context)
    {
      System.IO.MemoryStream ms = new System.IO.MemoryStream();
      Bitmap image = this.CreateImageCode(code);

      image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);

      context.Response.ClearContent();
      context.Response.ContentType = "image/Jpeg";
      context.Response.BinaryWrite(ms.GetBuffer());

      ms.Close();
      ms = null;
      image.Dispose();
      image = null;
    }

    #endregion

    #region 生成隨機字符碼

    public string CreateVerifyCode(int codeLen)
    {
      if (codeLen == 0)
      {
        codeLen = Length;
      }

      string[] arr = CodeSerial.Split(',');

      string code = "";

      int randValue = -1;

      Random rand = new Random(unchecked((int) DateTime.Now.Ticks));

      for (int i = 0; i  codeLen; i++)
      {
        randValue = rand.Next(0, arr.Length - 1);

        code += arr[randValue];
      }

      return code;
    }

    public string CreateVerifyCode()
    {
      return CreateVerifyCode(0);
    }

    #endregion
  }
}