asp.net写验证码

<%@ WebHandler Language="C#" Class="ValidataeCodeHandler" %>

using System;
using System.Web;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
using System.Drawing.Imaging;

public class ValidataeCodeHandler : IHttpHandler, System.Web.SessionState.IRequiresSessionState
{

    public void ProcessRequest(HttpContext context)
    {
        //请求类型：获取验证码图片，匹配验证码
        string type = context.Request["type"];

        if (type == "math")
        {
            if (string.IsNullOrEmpty(context.Request["code"]))
                context.Response.Write(2);
            else if (string.IsNullOrEmpty("" + context.Session["yqcode" + context.Request["id"]]))
            {
                context.Response.Write(3);
            }
            else
            {
                if ("" + context.Session["yqcode" + context.Request["id"]] == context.Request["code"] + "")
                    context.Response.Write(1);
                else
                    context.Response.Write(0);

            }
        }
        else
        {
            context.Response.ContentType = "image/gif";

            string validateCode = CreateValidateCode(context);//生成验证码 
            Bitmap bitmap = new Bitmap(imgWidth, imgHeight);//生成Bitmap图像 
            DisturbBitmap(bitmap); //图像背景 
            DrewValidateCode(bitmap, validateCode);//绘制验证码图像 
            bitmap.Save(context.Response.OutputStream, ImageFormat.Gif);//保存图像，等待输出 

            context.Response.Write(bitmap);
        }
    }



    //  private int codeLen = 4;//验证码长度 
    private int fineness = 85;//图片清晰度 
    private int imgWidth = 48;//图片宽度 
    private int imgHeight = 24;//图片高度 
    private string fontFamily = "Times New Roman";//字体名称 
    private int fontSize = 14;//字体大小 
    //private int fontStyle = 0;//字体样式 
    private int posX = 0;//绘制起始坐标X 
    private int posY = 0;//绘制坐标Y 
    private string CreateValidateCode(HttpContext context) //生成验证码 
    {
        string validateCode = "";
        Random random = new Random();// 随机数对象 
        validateCode = random.Next(1000, 9999) + "";
        //for (int i = 0; i < codeLen; i++)//循环生成每位数值 
        //{
        //    int n = random.Next(10);//数字 
        //    validateCode += n.ToString();
        //}
        context.Session["yqcode" + context.Request["id"]] = validateCode;//保存验证码 这Session是在前台调用的。
        return validateCode;// 返回验证码 
    }

    private void DisturbBitmap(Bitmap bitmap)//图像背景 
    {
        Random random = new Random();//通过随机数生成 
        for (int i = 0; i < bitmap.Width; i++)//通过循环嵌套，逐个像素点生成 
        {
            for (int j = 0; j < bitmap.Height; j++)
            {
                if (random.Next(90) <= this.fineness)
                    bitmap.SetPixel(i, j, Color.LightGray);
            }
        }
    }
    private void DrewValidateCode(Bitmap bitmap, string validateCode)//绘制验证码图像 
    {
        Graphics g = Graphics.FromImage(bitmap);//获取绘制器对象 
        Font font = new Font(fontFamily, fontSize, FontStyle.Bold);//设置绘制字体 
        g.DrawString(validateCode, font, Brushes.Black, posX, posY);//绘制验证码图像 
    }



    public bool IsReusable
    {
        get
        {
            return false;
        }
    }

}