如何调用?

在一个单独页面调用：
    protected void Page_Load(object sender, EventArgs e)
    {

//获取验证码的文字
        String  sContent = authcode.CreateImageOnPage(this.Context);   // 输出图片
    }

类文件:

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;

namespace HGZP.PLL
{
    /// <summary>
    /// 功能：验证码生成类
    /// 作者：许金杰
    /// 时间：2011.7.2
    /// </summary>

    public class authcode
    {
        #region 验证码长度
        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;//简介定义了图片大小：80px 160px
        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
        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";
        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 = PI * 3;
        /// <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="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.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);
                    // 取得当前点的颜色
                    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 生成校验码图片
        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();
            //给背景添加随机生成的燥点
            if (this.Chaos)
            {
                Random sjs = new Random();//产生随机数
                Pen pen = new Pen(Color.FromArgb(sjs.Next(255), sjs.Next(255), sjs.Next(255)), 2);
                //定义钢笔，用于绘制干扰线
                Pen pen1 = new Pen(Color.FromArgb(sjs.Next(255), sjs.Next(255), sjs.Next(255)), 1);
                Pen pen2 = new Pen(Color.FromArgb(sjs.Next(255), sjs.Next(255), sjs.Next(255)), 1);
                //生成两条横向的干扰线
                for (int i = 0; i < 4; i++)
                {
                    //定义起点
                    Point p1 = new Point(0, sjs.Next(image.Height));
                    //定义终点
                    Point p2 = new Point(image.Width, sjs.Next(image.Height));
                    //绘制直线
                    g.DrawLine(pen1, p1, p2);
                }
                //生成两条纵向的干扰线
                for (int i = 0; i < 4; i++)
                {
                    //定义起点
                    Point p1 = new Point(sjs.Next(image.Width), 0);
                    //定义终点
                    Point p2 = new Point(sjs.Next(image.Width), image.Height);
                    //绘制直线
                    g.DrawLine(pen2, p1, p2);
                }
                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;
            //随机字体和颜色的验证码字符
            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);
            }
            //画一个边框 边框颜色为Color.Gainsboro
            g.DrawRectangle(new Pen(Color.Gainsboro, 0), 0, 0, image.Width - 1, image.Height - 1);
            g.Dispose();
            //产生波形（Add By 51aspx.com）
            image = TwistImage(image, true, 8, 4);
            return image;
        }
        #endregion
        #region 将创建好的图片输出到页面并返回随机数
        public static string CreateImageOnPage(HttpContext context)
        {
            authcode aa = new authcode();
            string code = aa.CreateCode();
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            Bitmap image = aa.CreateImageCode(code);
            image.Save(ms, ImageFormat.Jpeg);//图片保存在指定流中
            context.Response.ClearContent();
            context.Response.ContentType = "image/Jpeg";
            context.Response.BinaryWrite(ms.GetBuffer());
            ms.Close();
            ms = null;
            image.Dispose();
            image = null;
            return code;
        }
        #endregion
        #region 生成随机字符码
        public string CreateCode()
        {
            int 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;
        }
        #endregion
    }
}