要实现如图的效果的验证码，分以下步骤：

第一、布局好调用验证码的登录页面（命名：Login.aspx），注意：验证码位置可以是服务器控件 Image，也可以是html标签写的<img>，但是图片url就是一个页面（命名：ValidateCode.aspx）(将在下面讲述。)比如：<asp:Image ID=“vcImg”      ImageUrl="~/ValidateCode.aspx"   runat="server" />

第二、生成类文件 (命名：validatedCode）

using System;
using System.Data;
using System.Configuration;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;

/// <summary>
/// Summary description for validatedCode
/// </summary>
public class validatedCode
{   
       #region  验证码长度(默认6个验证码的长度)
        int length = 4;
        public int Length
        {
            get { return length; }
            set { length = value; }
        }
        #endregion

        #region 验证码字体大小(为了显示扭曲效果，默认40像素，可以自行修改)
        int fontSize = 40;
        public int FontSize
        {
            get { return fontSize; }
            set { fontSize = value; }
        }
        #endregion

        #region 边框补(默认1像素)
        int padding = 2;
        public int Padding
        {
            get { return padding; }
            set { padding = value; }
        }
        #endregion

        #region 是否输出燥点(默认不输出)
        bool chaos = true;
        public bool Chaos
        {
            get { return chaos; }
            set { chaos = value; }
        }
        #endregion

        #region 输出燥点的颜色(默认灰色)
        Color chaosColor = Color.LightGray;
        public Color ChaosColor
        {
            get { return chaosColor; }
            set { chaosColor = value; }
        }
        #endregion

        #region 自定义背景色(默认白色)
        Color backgroundColor = Color.White;
        public Color BackgroundColor
        {
            get { return backgroundColor; }
            set { backgroundColor = value; }
        }
        #endregion

        #region 自定义随机颜色数组
        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 自定义字体数组
        string[] fonts = { "Arial", "Georgia" };
        public string[] Fonts
        {
            get { return fonts; }
            set { fonts = value; }
        }
        #endregion

        #region 自定义随机码字符串序列(使用逗号分隔)
        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";
        public string CodeSerial
        {
            get { return codeSerial; }
            set { codeSerial = value; }
        }
        #endregion

        #region 产生波形滤镜效果

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

        /// <summary>
        /// 正弦曲线Wave扭曲图片（Edit By 51aspx.com）
        /// </summary>
        /// <param name="srcBmp">图片路径</param>
        /// <param name="bXDir">如果扭曲则选择为True</param>
        /// <param name="nMultValue">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>
        /// <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);

            // 将位图背景填充为白色
            System.Drawing.Graphics graph = System.Drawing.Graphics.FromI