c# 验证码的实现

1.<img src="Yanzhengma.aspx" onclick="this.src='Yanzhengma.aspx?'+Math.random()" title="看不清，换一张？" height="25px"/>--验证码显示页面

2.后台获取验证码：string yanzhengma = Session["Checkcode"].ToString();

3.验证码页面：

using System;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Web;
using System.Web.SessionState;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Text;
using AjaxControlToolkit;

public partial class Yanzhengma : System.Web.UI.Page
{

    public static string SESSION_VALICATE = "{D9B583D0-9760-4687-908C-A109E3498E59}";

    protected void Page_Load(object sender, EventArgs e)
    {
        Response.Cache.SetCacheability(System.Web.HttpCacheability.NoCache);
        Response.AddHeader("P3P", "CP=CAO PSA OUR");

       
       
            Session["Checkcode"] = CreateCheckCode(4, 2);
       
    }

    #region Web 窗体设计器生成的代码
    override protected void OnInit(EventArgs e)
    {
        //
        // CODEGEN: 该调用是 ASP.NET Web 窗体设计器所必需的。
        //
        InitializeComponent();
        base.OnInit(e);
    }

    /// <summary>
    /// 设计器支持所需的方法 - 不要使用代码编辑器修改
    /// 此方法的内容。
    /// </summary>
    private void InitializeComponent()
    {

    }
    #endregion

    /// <summary>
    /// 创建验证码,返回验证码字符串
    /// </summary>
    /// <param name="CodeLen">int CodeLe:验证码长度</param>
    /// <param name="CodeType">int CodeType:0纯数字;1纯字母;2数字与字母混合;3纯汉字</param>
    /// <returns></returns>
    ///
    private string CreateCheckCode(int CodeLen, int CodeType)
    {
        /**参数说明：CodeLen(验证码长度）;CodeType(0纯数字，1纯字母,2,数字与字母混合，3,纯汉字)**/
       
        CodeType = 0;
        string codestring = "";
        //定义验证图片的长度与宽度
        int Clen = 30 * CodeLen, Cheight = 40;
        //定义验证图片的背景颜色
        Color CBcolor = Color.FromArgb(150, 180, 70);
        string[] font = { "Bell MT", "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体", "幼圆", "楷体_GB2312", "仿宋_GB2312" };
        Font Cfont = new Font("Arial", 20, FontStyle.Italic);
        //产生随机验证码---------------------------------------------------------------------------------------------------
        switch (CodeType)
        {
            //纯数字
            case 0:
                Random random1 = new Random();
                codestring = random1.Next((int)System.Math.Pow(10, CodeLen - 1), (int)System.Math.Pow(10, CodeLen) - 1).ToString();
                break;
            //纯数字
            //纯字母
            case 1:
                string Vchar1 = "A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,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[] VcArray1 = Vchar1.Split(',');
                int vclen1 = VcArray1.Length;
                int vcindex1;
                Random random2 = new Random();
                for (int i = 0; i < CodeLen; i++)
                {
                    vcindex1 = random2.Next(vclen1);
                    codestring = codestring + VcArray1[vcindex1];
                }
                break;
            case 2:
                string Vchar2 = "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,W,X,Y,Z,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";
                String[] VcArray2 = Vchar2.Split(',');
                int vclen2 = VcArray2.Length;
                int vcindex2;
                Random random3 = new Random();
                for (int i = 0; i < CodeLen; i++)
                {
                    vcindex2 = random3.Next(vclen2);
                    codestring = codestring + VcArray2[vcindex2];
                }
                break;
            //纯字母
            //纯汉字
            case 3:
                //定义一个字符串数组储存汉字编码的组成元素
                string[] rBase = new String[16] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "a", "b", "c", "d", "e", "f" };
                Random rnd = new Random();
                int strlength = CodeLen * 2;
                //定义一个object数组用来
                object[] bytes = new object[strlength];
                /**/
                /*每循环一次产生一个含两个元素的十六进制字节数组，并将其放入bject数组中
                每个汉字有四个区位码组成
                区位码第1位和区位码第2位作为字节数组第一个元素
                区位码第3位和区位码第4位作为字节数组第二个元素
                */
                for (int i = 0; i < strlength; i++)
                {
                    //区位码第1位
                    int r1 = rnd.Next(11, 14);
                    string str_r1 = rBase[r1].Trim();
                    //区位码第2位
                    rnd = new Random(r1 * unchecked((int)DateTime.Now.Ticks) + i);//更换随机数发生器的种子避免产生重复值
                    int r2;
                    if (r1 == 13)
                    {
                        r2 = rnd.Next(0, 7);
                    }
                    else
                    {
                        r2 = rnd.Next(0, 16);
                    }
                    string str_r2 = rBase[r2].Trim();
                    //区位码第3位
                    rnd = new Random(r2 * unchecked((int)DateTime.Now.Ticks) + i);
                    int r3 = rnd.Next(10, 16);
                    string str_r3 = rBase[r3].Trim();
                    //区位码第4位
                    rnd = new Random(r3 * unchecked((int)DateTime.Now.Ticks) + i);
                    int r4;
                    if (r3 == 10)
                    {
                        r4 = rnd.Next(1, 16);
                    }
                    else if (r3 == 15)
                    {
                        r4 = rnd.Next(0, 15);
                    }
                    else
                    {
                        r4 = rnd.Next(0, 16);
                    }
                    string str_r4 = rBase[r4].Trim();
                    //定义两个字节变量存储产生的随机汉字区位码
                    byte byte1 = Convert.ToByte(str_r1 + str_r2, 16);
                    byte byte2 = Convert.ToByte(str_r3 + str_r4, 16);
                    //将两个字节变量存储在字节数组中
                    byte[] str_r = new byte[] { byte1, byte2 };
                    //将产生的一个汉字的字节数组放入object数组中
                    bytes.SetValue(str_r, i);
                }
                Encoding gb = Encoding.GetEncoding("gb2312");
                //根据汉字编码的字节数组解码出中文汉字
                for (int i = 0; i < strlength / 2; i++)
                {
                    codestring = codestring + gb.GetString((byte[])Convert.ChangeType(bytes[i], typeof(byte[])));
                }
                break;
            //纯汉字
        }

 

        //显示验证码-----------------------------------------------------------------------------------------------------
        //创建一个图像
        //定义画笔，用于绘制文字
        Brush brush1 = new SolidBrush(Color.Black);
        Bitmap bitmap1 = new System.Drawing.Bitmap(Clen, Cheight);
        //从图像获取一个绘画面
        Graphics graphics1 = Graphics.FromImage(bitmap1);
        //清除整个绘图画面并用颜色填充
        graphics1.Clear(CBcolor);
        PointF Cpoint1 = new PointF(5, 5);
        Random rnd1 = new Random();
        int x1 = 0, y1 = 0;
        //绘制边框
        graphics1.DrawRectangle(new Pen(Color.Silver), 0, 0, bitmap1.Width - 1, bitmap1.Height - 1);
        //绘制文字
        for (int i = 0; i < codestring.Length; i++)
        {
            //随机字符位置
            x1 = rnd1.Next(10) + 25 * i;
            y1 = rnd1.Next(bitmap1.Height / 4);
            Cpoint1 = new PointF(x1, y1);
            //随机字符颜色,应根据背景作适当调整以免显示模糊不清
            brush1 = new SolidBrush(Color.FromArgb(rnd1.Next(100), rnd1.Next(100), rnd1.Next(100)));
            Cfont = new Font(font[rnd1.Next(font.Length - 1)], 24, FontStyle.Bold);
            //随机倾斜字符
            graphics1.TranslateTransform(5, 0);
            Matrix transform = graphics1.Transform;
            transform.Shear(Convert.ToSingle(rnd1.NextDouble() - 0.5), 0.001f);
            graphics1.Transform = transform;
            graphics1.DrawString(codestring.Substring(i, 1), Cfont, brush1, Cpoint1);
            graphics1.ResetTransform();
        }

        //绘制干扰点
        rnd1 = new Random();
        for (int i = 0; i < 1 * CodeLen; i++)
        {
            //随机干扰位置
            x1 = rnd1.Next(bitmap1.Width);
            y1 = rnd1.Next(bitmap1.Height);
            bitmap1.SetPixel(x1, y1, Color.FromArgb(rnd1.Next(50), rnd1.Next(50), rnd1.Next(50)));
        }

        //绘制干扰线
        rnd1 = new Random();
        for (int i = 0; i < 2; i++)
        {
            //随机干扰位置
            x1 = rnd1.Next(bitmap1.Width);
            y1 = rnd1.Next(bitmap1.Height);
            int x2 = rnd1.Next(bitmap1.Width);
            int y2 = rnd1.Next(bitmap1.Height);
            //随机干扰线颜色
            Pen pen1 = new Pen(Color.FromArgb(rnd1.Next(100, 255), rnd1.Next(100, 255), rnd1.Next(100, 255)));
            graphics1.DrawLine(pen1, x1, y1, x2, y2);
        }
        bitmap1.Save(Response.OutputStream, ImageFormat.Jpeg);
        bitmap1.Dispose();
        graphics1.Dispose();
        return codestring;
    }
}