验证码

<td>
                        <label>验证码：</label>
                        <input class="code" id="CheckCode" type="text" size="5" runat="server" />
                        <a href="#" style="outline:none" title="点击更换验证码"  onclick="document.getElementById('getcode').src='Image.aspx?temp='+ (new Date().getTime().toString(36)); return false">
                        <span><img src="image.aspx" id="getcode" alt="" width="75" height="24" />
                        </span></a>
                     </td>

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;

public partial class Image : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
         
            string str_ValidateCode = RndNum(4);            //  用于验证的Session          
            Session["ValidateCode"] = str_ValidateCode;      
            CreateImages(str_ValidateCode); 
    }
    /// <summary>
    /// 生成验证字符
    /// </summary>
    /// <param name="checkCode"></param>
    private void CreateImages(string checkCode)
    {
        int iwidth = (int)(checkCode.Length  * 15);
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);
        Graphics g = Graphics.FromImage(image);
        g.Clear(Color.White);
        //定义颜色
        //Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
        /,修改定义颜色数组个数，去掉橙色，
        Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Brown, Color.DarkCyan, Color.Purple };

        //定义字体 
        string[] font = {"Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体"};
        Random rand = new Random();
        //随机输出噪点
        for (int i = 0; i < 50; i++)
        {
            int x = rand.Next(image.Width);
            int y = rand.Next(image.Height);
            g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);
        }

        //输出不同字体和颜色的验证码字符
        for (int i = 0; i < checkCode.Length; i++)
        {
            int cindex = rand.Next(6);//小于7,输出的个数小于定义的字体数组个数
            int findex = rand.Next(5);//小于5

            Font f = new System.Drawing.Font(font[findex], 13, System.Drawing.FontStyle.Bold);//下标为5的字体,13
            Brush b = new System.Drawing.SolidBrush(c[cindex]);//颜色为pruple
            int ii = 6;
            if ((i + 1) % 2 == 0)
            {
                ii = 4;
            }
            g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * 16), ii);//字符串，文本样式，背景文理，x,y坐标
        }
        //画一个边框
        g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width-1 , image.Height-1);

        //输出到浏览器
        System.IO.MemoryStream ms = new System.IO.MemoryStream();

        image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);
        HttpContext.Current.Response.ClearContent();
        //Response.ClearContent();
        HttpContext.Current.Response.ContentType = "image/Jpeg";
        HttpContext.Current.Response.BinaryWrite(ms.ToArray());
        g.Dispose();
        image.Dispose();
    }

    /// <summary>
    /// 生成随机字符
    /// </summary>
    /// <param name="VcodeNum">验证码的个数</param>
    /// <returns></returns>
    private string RndNum(int VcodeNum)
    {
        //string Vchar = "1,2,3,4,5,6,7,8,9";
        string Vchar = "1";
        //Vchar += ",a,b,c,d,e,f,g,h,i,j,k,l,m,n,p,q,r,s,t,u,v,w,x,y,z";
        //Vchar += ",A,B,C,D,E,F,G,H,I,J,K,L,M,N,P,Q,R,S,T,U,V,W,X,Y,Z";
        Vchar += ",i,j,l,r";
        Vchar += ",I,J,L,R";
        string[] VcArray = Vchar.Split(',');
        string VNum = ""; //由于字符串很短，就不用StringBuilder了
        int temp = -1; //记录上次随机数值，尽量避免生产几个一样的随机数

        //采用一个简单的算法以保证生成随机数的不同
        Random rand = new Random();
        for (int i = 1; i < VcodeNum + 1; i++)
        {
            if (temp != -1)
            {
                rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));
            }
            int t = rand.Next(VcArray.Length);
            if (temp != -1 && temp == t)
            {
                return RndNum(VcodeNum);
            }
            temp = t;
            VNum += VcArray[t];
        }
        return VNum;
    }
}