如何制作验证码？
就是那种字母数字印在图片上的那种？

[解决办法]
private string GetCode(int num)
{
string[] source ={ "1", "2", "3", "4", "5", "6", "7", "8", "9", "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", "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 code = "";
Random rd = new Random();
for (int i = 0; i < num; i++)
{
code += source[rd.Next(0, source.Length)];
}
return code;
}
private MemoryStream GetVImageStream()
{
MemoryStream ImageMemoryStream = new MemoryStream();
string VCodeString = GetCode(4);
Session["HCValidateCode"] = VCodeString;
Font VCodeFont = new Font("Arial", 14, FontStyle.Bold);
SolidBrush VCodeBrush = new SolidBrush(Color.SandyBrown);
Pen LinePen = new Pen(Color.Ivory, 1);
Bitmap Tmap = new Bitmap(VCodeString.Length * 19, 24);
Graphics TGrphics;
TGrphics = Graphics.FromImage(Tmap);
TGrphics.Clear(BackGroundColor(0, 255));
//产生干扰线
for (int i = 1; i <= 6; i++)
{
int TmpPosition = i * 4;
Color LineColor = BackGroundColor(0, 255);
LinePen.Color = LineColor;
TGrphics.DrawLine(LinePen, 0, TmpPosition, VCodeString.Length * 19, 0);
LineColor = BackGroundColor(0, 255);
LinePen.Color = LineColor;
TGrphics.DrawLine(LinePen, 0, 24, VCodeString.Length * 19, TmpPosition);
}
//产生干扰线
TGrphics.DrawString(VCodeString, VCodeFont, VCodeBrush, VCodeString.Length, 1);
Tmap.Save(ImageMemoryStream, System.Drawing.Imaging.ImageFormat.Png);
Tmap.Dispose();
TGrphics.Dispose();
return ImageMemoryStream;
}

#region 随机返回背景色
/// <summary>
/// 随机返回颜色
/// </summary>
/// <param name="BeginRandomNumber">指定颜色开始的最小值 </param>
/// <param name="RandomNumber">指定颜色值波动的范围 </param>
/// <returns>随机的Color </returns>
private Color BackGroundColor( int BeginRandomNumber , int RandomNumber )
{
int ColorR = 0 ;
int ColorG = 0 ;
int ColorB = 0 ;
Random TRandom = new Random() ;
ColorR = BeginRandomNumber + TRandom.Next( RandomNumber ) ;
ColorG = BeginRandomNumber + TRandom.Next( RandomNumber ) ;
ColorB = BeginRandomNumber + TRandom.Next( RandomNumber ) ;
Color ColorBG = Color.FromArgb( ColorR , ColorG , ColorB ) ;
return ColorBG ;
}
#endregion


Response.ClearContent();

Response.ContentType = "images/Png";
Response.BinaryWrite(GetVImageStream().ToArray());
[解决办法]
using System;
using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Text;
using System.Collections;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
/**//// <summary>
///
/// ** asp.net(C#) 生成验证码 **
///
/// File: GenerateCheckCode.aspx.cs
///
/// Author: 周振兴 (Zxjay 飘遥)
///
/// E-Mail: tda7264@163.com
///
/// Date: 07-04-10
///
/// </summary>
public partial class GenerateCheckCode : System.Web.UI.Page
...{
protected void Page_Load(object sender, EventArgs e)
...{
string chkCode = string.Empty;
//颜色列表，用于验证码、噪线、噪点
Color[] color =...{ Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue };
//字体列表，用于验证码
string[] font =...{ "Times New Roman", "MS Mincho", "Book Antiqua", "Gungsuh", "PMingLiU", "Impact" };
//验证码的字符集，去掉了一些容易混淆的字符
char[] character =...{ '2', '3', '4', '5', '6', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y' };
Random rnd = new Random();
//生成验证码字符串
for (int i = 0; i < 4; i++)
...{
chkCode += character[rnd.Next(character.Length)];
}
Bitmap bmp = new Bitmap(100, 40);
Graphics g = Graphics.FromImage(bmp);
g.Clear(Color.White);
//画噪线
for (int i = 0; i < 10; i++)
...{
int x1 = rnd.Next(100);
int y1 = rnd.Next(40);
int x2 = rnd.Next(100);
int y2 = rnd.Next(40);
Color clr = color[rnd.Next(color.Length)];
g.DrawLine(new Pen(clr), x1, y1, x2, y2);
}
//画验证码字符串
for (int i = 0; i < chkCode.Length; i++)
...{
string fnt = font[rnd.Next(font.Length)];
Font ft = new Font(fnt, 18);
Color clr = color[rnd.Next(color.Length)];
g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 20 + 8, (float)8);
}
//画噪点
for (int i = 0; i < 100; i++)
...{
int x = rnd.Next(bmp.Width);
int y = rnd.Next(bmp.Height);
Color clr = color[rnd.Next(color.Length)];
bmp.SetPixel(x, y, clr);
}
//清除该页输出缓存，设置该页无缓存
Response.Buffer = true;
Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0);
Response.Expires = 0;
Response.CacheControl = "no-cache";
Response.AppendHeader("Pragma", "No-Cache");
//将验证码图片写入内存流，并将其以 "image/Png" 格式输出
MemoryStream ms = new MemoryStream();
try
...{
bmp.Save(ms, ImageFormat.Png);
Response.ClearContent();
Response.ContentType = "image/Png";
Response.BinaryWrite(ms.ToArray());
}
finally
...{
//显式释放资源
bmp.Dispose();
g.Dispose();
}
}
}



使用方法如下：
新建名为 GenerateCheckCode.aspx 的文件，将上述代码拷贝到代码文件 GenerateCheckCode.aspx.cs
在需要验证码的地方放置语句 <asp:Image ID="img1" runat="server" ImageUrl="~/GenerateCheckCode.aspx" /> 即可。

[解决办法]
http://web.tiens.com/temp/verify.rar
给你做好了，现成的
用时用<img src=verify.aspx>就可以了