验证码：                                                                                                                     

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);     }    /// 
    /// 生成验证字符    /// 
    ///     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();    }    /// 
    /// 生成随机字符    /// 
    /// 验证码的个数    /// 
         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;    }}