asp.net 加入验证码

验证码生成页面代码（清理掉没用的html）

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
using System.Threading;
using System.Drawing.Text;
using System.Drawing.Drawing2D;

namespace ZhuoYueE.Dop.Web.UI.FenFa
{
    public partial class CodeImg : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            string randomcode = CreateRandomCode();
            Session["Code"] = randomcode;
            this.CreateImage(randomcode);
        }

        /// 生成随机码
        /// </summary>
        /// <param name="length">随机码个数</param>
        /// <returns></returns>
        private string CreateRandomCode(int length)
        {
            int rand;
            char code;
            string randomcode = String.Empty;

            //生成一定长度的验证码
            System.Random random = new Random();
            for (int i = ; i < length; i++)
            {
            start:
                rand = random.Next();

                if (rand %  == )
                {
                    code = (char)('A' + (char)(rand % ));
                }
                else
                {
                    code = (char)('' + (char)(rand % ));
                }
                if (code == '' || code == 'o' || code == 'O' || code == '' || code == 'i' || code == 'I' || code == 'l')
                    goto start;
                randomcode += code.ToString();
            }
            return randomcode;
        }

        /// <summary>
        /// 创建随机码图片
        /// </summary>
        /// <param name="randomcode">随机码</param>
        private void CreateImage(string randomcode)
        {
            //定义颜色
            Random rand = new Random();

            Color c = Color.FromArgb(rand.Next(), rand.Next(), rand.Next());

            int randAngle = ; //随机转动角度
            int mapwidth = (int)(randomcode.Length * );
            Bitmap map = new Bitmap(mapwidth, );//创建图片背景
            Graphics graph = Graphics.FromImage(map);
            graph.Clear(Color.FromArgb(rand.Next(, ), rand.Next(, ), rand.Next(, )));//清除画面，填充背景
            graph.DrawRectangle(new Pen(Color.Black, ), , , map.Width - , map.Height - );//画一个边框
            //graph.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.AntiAlias;//模式

            //背景噪点生成
            //Pen blackPen = new Pen(c[cindex], 0);
            //for (int i = 0; i < 30; i++)
            //{
            //    int x = rand.Next(0, map.Width);
            //    int y = rand.Next(0, map.Height);
            //    graph.DrawRectangle(blackPen, x, y, 1, 1);
            //}

            //验证码旋转，防止机器识别
            char[] chars = randomcode.ToCharArray();//拆散字符串成单字符数组

            //文字距中
            StringFormat format = new StringFormat(StringFormatFlags.NoClip);
            format.Alignment = StringAlignment.Center;
            format.LineAlignment = StringAlignment.Center;

            //定义字体
            string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体", "Microsoft New Tai Lue" };

            int Count = font.Length;

            LinearGradientBrush b = new LinearGradientBrush(
                  new Point(, ), new Point(, ),
                  Color.FromArgb(rand.Next(), rand.Next(), rand.Next()),
                  Color.FromArgb(rand.Next(), rand.Next(), rand.Next()));

            for (int i = ; i < chars.Length; i++)
            {
                int findex = rand.Next(Count);

                //渐变色：起点（0, 0)从红色 --->终点(250, 250)蓝色

                Font f = new System.Drawing.Font(font[findex], , System.Drawing.FontStyle.Bold);//字体样式(参数2为字体大小)

                // Brush b = new System.Drawing.SolidBrush(c);

                Point dot = new Point(, );
                //graph.DrawString(dot.X.ToString(),fontstyle,new SolidBrush(Color.Black),10,150);//测试X坐标显示间距的
                float angle = rand.Next(-randAngle, randAngle);//转动的度数

                graph.TranslateTransform(dot.X, dot.Y);//移动光标到指定位置
                graph.RotateTransform(angle);
                graph.DrawString(chars[i].ToString(), f, b, , , format);
                //graph.DrawString(chars[i].ToString(),fontstyle,new SolidBrush(Color.Blue),1,1,format);
                graph.RotateTransform(-angle);//转回去
                graph.TranslateTransform(-, -dot.Y);//移动光标到指定位置，每个字符紧凑显示，避免被软件识别
            }

            //画干扰线
            Graphics graph1 = Graphics.FromImage(map);
            int intw = map.Width / ;
            int inth = map.Height / ;
            for (int i = ; i < ; i++)
            {
                int x1, x2, y1, y2;
                x1 = rand.Next(, intw);
                y1 = rand.Next(inth, map.Height - inth);
                Thread.Sleep();
                x2 = rand.Next(map.Width - intw, map.Width);
                Thread.Sleep();
                y2 = rand.Next(inth, map.Height - inth);
                graph1.DrawLine(new Pen(b, 1f), x1, y1, x2, y2);
            }

            for (int i = ; i < map.Width; i++)
            {
                for (int j = ; j < map.Height; j++)
                {
                    Color cc = map.GetPixel(i, j);
                    map.SetPixel(i, j, GetColorByColor(cc));
                }
            }

            //生成图片
            System.IO.MemoryStream ms = new System.IO.MemoryStream();
            map.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            Response.ClearContent();
            Response.ContentType = "image/gif";
            Response.BinaryWrite(ms.ToArray());
            graph.Dispose();
            graph1.Dispose();
            map.Dispose();
        }

        private Color GetColorByColor(Color c)
        {
            int[] cs = new int[] { c.R, c.G, c.B };
            Random r = new Random();
            for (int i = ; i < cs.Length; i++)
            {
                if (cs[i] <  || cs[i] > )
                    continue;
                int rn = r.Next(-, );
                cs[i] += rn;
            }
            return Color.FromArgb(cs[], cs[], cs[]);
        }
    }
}

调用代码

<img style="height: 30px" src="codeimg.aspx" id="imgcode" onclick="GetCode()" />

 function GetCode() {
            document.getElementById("imgcode").src = "codeimg.aspx?t=" + new Date().getTime();
        }

　　效果如下：