为了应付越来越多的自动发帖机、恶意攻击等情形，验证码技术在大量的网站上得到使用。我在近期开发一个注册网站的时候，也使用了这一技术。当然，我并不想完完全全自己重新实现，而是参考了网上能够找到的实现，做了若干改进而已。下面谈谈我的实现。
补两张图片：
首先看验证码图片输出页的代码：
<%@ Page Language="C#" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
VryImgGen gen = new VryImgGen();
string verifyCode = gen.CreateVerifyCode(5, 1);
Session["VerifyCode"] = verifyCode.ToUpper();
System.Drawing.Bitmap bitmap = gen.CreateImage(verifyCode);
System.IO.MemoryStream ms = new System.IO.MemoryStream();
bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
Response.Clear();
Response.ContentType = "image/Png";
Response.BinaryWrite(ms.GetBuffer());
bitmap.Dispose();
ms.Dispose();
ms.Close();
Response.End();
}
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
VryImgGen gen = new VryImgGen();
string verifyCode = gen.CreateVerifyCode(5, 1);
Session["VerifyCode"] = verifyCode.ToUpper();
System.Drawing.Bitmap bitmap = gen.CreateImage(verifyCode);
System.IO.MemoryStream ms = new System.IO.MemoryStream();
bitmap.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
Response.Clear();
Response.ContentType = "image/Png";
Response.BinaryWrite(ms.GetBuffer());
bitmap.Dispose();
ms.Dispose();
ms.Close();
Response.End();
}
</script>
功能很简单，初始化一个验证码生成对象，生成图片。然后保存到一个MemoryStream里。得到字节流，输出字节流。验证码的数据是保存在Session中的，这是最简单的方法。或者可以加密储存在cookie里，也是可以的。
再来看看验证码生成对象：
using System;
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Text;
/// <summary>
/// Summary description for VryImgGen
/// </summary>
public partial class VryImgGen
{
/// <summary>
/// 供验证码生成汉字时选取的汉字集,若为空则按照《GB2312简体中文编码表》编码规则构造汉字
/// </summary>
public static string ChineseChars = String.Empty;
/// <summary>
/// 英文与数字串
/// </summary>
protected static readonly string EnglishOrNumChars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
public VryImgGen()
{
rnd = new Random(unchecked((int)DateTime.Now.Ticks));
}
/// <summary>
/// 全局随机数生成器
/// </summary>
private Random rnd;
int length = 5;
/// <summary>
/// 验证码长度(默认6个验证码的长度)
/// </summary>
public int Length
{
get { return length; }
set { length = value; }
}
int fontSize = 18;
/// <summary>
/// 验证码字体大小(为了显示扭曲效果，默认30像素，可以自行修改)
/// </summary>
public int FontSize
{
get { return fontSize; }
set { fontSize = value; }
}
int padding = 4;
/// <summary>
/// 边框补(默认4像素)
/// </summary>
public int Padding
{
get { return padding; }
set { padding = value; }
}
bool chaos = true;
/// <summary>
/// 是否输出燥点(默认输出)
/// </summary>
public bool Chaos
{
get { return chaos; }
set { chaos = value; }
}
Color chaosColor = Color.LightGray;
/// <summary>
/// 输出燥点的颜色(默认灰色)
/// </summary>
public Color ChaosColor
{
get { return chaosColor; }
set { chaosColor = value; }
}
Color backgroundColor = Color.White;
/// <summary>
/// 自定义背景色(默认白色)
/// </summary>
public Color BackgroundColor
{
get { return backgroundColor; }
set { backgroundColor = value; }
}
Color[] colors = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
/// <summary>
/// 自定义随机颜色数组
/// </summary>
public Color[] Colors
{
get { return colors; }
set { colors = value; }
}
string[] fonts = { "Arial", "Georgia" };
/// <summary>
/// 自定义字体数组
/// </summary>
public string[] Fonts
{
get { return fonts; }
set { fonts = value; }
}
#region 产生波形滤镜效果
private const double PI = 3.1415926535897932384626433832795;
private const double PI2 = 6.283185307179586476925286766559;
/// <summary>
/// 正弦曲线Wave扭曲图片（Edit By 51aspx.com）
/// </summary>
/// <param name="srcBmp">图片路径</param>
/// <param name="bXDir">如果扭曲则选择为True</param>
/// <param name="nMultValue">波形的幅度倍数，越大扭曲的程度越高，一般为3</param>
/// <param name="dPhase">波形的起始相位，取值区间[0-2*PI)</param>
/// <returns></returns>
public System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
{
System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
// 将位图背景填充为白色
System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp);
graph.FillRectangle(new SolidBrush(System.Drawing.Color.White), 0, 0, destBmp.Width, destBmp.Height);
graph.Dispose();
double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
for (int i = 0; i < destBmp.Width; i++)
{
for (int j = 0; j < destBmp.Height; j++)
{
double dx = 0;
dx = bXDir ? (PI2 * (double)j) / dBaseAxisLen : (PI2 * (double)i) / dBaseAxisLen;
dx += dPhase;
double dy = Math.Sin(dx);
// 取得当前点的颜色
int nOldX = 0, nOldY = 0;
nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
nOldY = bXDir ? j : j + (int)(dy * dMultValue);
System.Drawing.Color color = srcBmp.GetPixel(i, j);
if (nOldX >= 0 && nOldX < destBmp.Width
&& nOldY >= 0 && nOldY < destBmp.Height)
{
destBmp.SetPixel(nOldX, nOldY, color);
}
}
}
return destBmp;
}
#endregion
/// <summary>
/// 生成校验码图片
/// </summary>
/// <param name="code">验证码</param>
/// <returns></returns>
public Bitmap CreateImage(string code)
{
int fSize = FontSize;
int fWidth = fSize + Padding;
int imageWidth = (int)(code.Length * fWidth) + 4 + Padding * 2;
int imageHeight = fSize * 2 + Padding * 2;
System.Drawing.Bitmap image = new System.Drawing.Bitmap(imageWidth, imageHeight);
Graphics g = Graphics.FromImage(image);
g.Clear(BackgroundColor);
//给背景添加随机生成的燥点
if (this.Chaos)
{
Pen pen = new Pen(ChaosColor, 0);
int c = Length * 10;
for (int i = 0; i < c; i++)
{
int x = rnd.Next(image.Width);
int y = rnd.Next(image.Height);
g.DrawRectangle(pen, x, y, 1, 1);
}
}
int left = 0, top = 0, top1 = 1, top2 = 1;
int n1 = (imageHeight - FontSize - Padding * 2);
int n2 = n1 / 4;
top1 = n2;
top2 = n2 * 2;
Font f;
Brush b;
int cindex, findex;
//随机字体和颜色的验证码字符
for (int i = 0; i < code.Length; i++)
{
cindex = rnd.Next(Colors.Length - 1);
findex = rnd.Next(Fonts.Length - 1);
f = new System.Drawing.Font(Fonts[findex], fSize, System.Drawing.FontStyle.Bold);
b = new System.Drawing.SolidBrush(Colors[cindex]);
if (i % 2 == 1)
{
top = top2;
}
else
{
top = top1;
}
left = i * fWidth;
g.DrawString(code.Substring(i, 1), f, b, left, top);
}
//画一个边框 边框颜色为Color.Gainsboro
g.DrawRectangle(new Pen(Color.Gainsboro, 0), 0, 0, image.Width - 1, image.Height - 1);
g.Dispose();
//产生波形（Add By 51aspx.com）
image = TwistImage(image, true, 8, 4);
return image;
}
/// <summary>
/// 生成随机字符码
/// </summary>
/// <param name="codeLen">字符串长度</param>
/// <param name="zhCharsCount">中文字符数</param>
/// <returns></returns>
public string CreateVerifyCode(int codeLen, int zhCharsCount)
{
char[] chs = new char[codeLen];
int index;
for (int i = 0; i < zhCharsCount; i++)
{
index = rnd.Next(0, codeLen);
if (chs[index] == '\0')
chs[index] = CreateZhChar();
else
--i;
}
for (int i = 0; i < codeLen; i++)
{
if (chs[i] == '\0')
chs[i] = CreateEnOrNumChar();
}
return new string(chs, 0, chs.Length);
}
/// <summary>
/// 生成默认长度5的随机字符码
/// </summary>
/// <returns></returns>
public string CreateVerifyCode()
{
return CreateVerifyCode(Length, 0);
}
/// <summary>
/// 生成英文或数字字符
/// </summary>
/// <returns></returns>
protected char CreateEnOrNumChar()
{
return EnglishOrNumChars[rnd.Next(0, EnglishOrNumChars.Length)];
}
/// <summary>
/// 生成汉字字符
/// </summary>
/// <returns></returns>
protected char CreateZhChar()
{
//若提供了汉字集，查询汉字集选取汉字
if (ChineseChars.Length > 0)
{
return ChineseChars[rnd.Next(0, ChineseChars.Length)];
}
//若没有提供汉字集，则根据《GB2312简体中文编码表》编码规则构造汉字
else
{
byte[] bytes = new byte[2];
//第一个字节值在0xb0, 0xf7之间
bytes[0] = (byte)rnd.Next(0xb0, 0xf8);
//第二个字节值在0xa1, 0xfe之间
bytes[1] = (byte)rnd.Next(0xa1, 0xff);
//根据汉字编码的字节数组解码出中文汉字
string str1 = Encoding.GetEncoding("gb2312").GetString(bytes);
return str1[0];
}
}
}
using System.Data;
using System.Configuration;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.Text;
/// <summary>
/// Summary description for VryImgGen
/// </summary>
public partial class VryImgGen
{
/// <summary>
/// 供验证码生成汉字时选取的汉字集,若为空则按照《GB2312简体中文编码表》编码规则构造汉字
/// </summary>
public static string ChineseChars = String.Empty;
/// <summary>
/// 英文与数字串
/// </summary>
protected static readonly string EnglishOrNumChars = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
public VryImgGen()
{
rnd = new Random(unchecked((int)DateTime.Now.Ticks));
}
/// <summary>
/// 全局随机数生成器
/// </summary>
private Random rnd;
int length = 5;
/// <summary>
/// 验证码长度(默认6个验证码的长度)
/// </summary>
public int Length
{
get { return length; }
set { length = value; }
}
int fontSize = 18;
/// <summary>
/// 验证码字体大小(为了显示扭曲效果，默认30像素，可以自行修改)
/// </summary>
public int FontSize
{
get { return fontSize; }
set { fontSize = value; }
}
int padding = 4;
/// <summary>
/// 边框补(默认4像素)
/// </summary>
public int Padding
{
get { return padding; }
set { padding = value; }
}
bool chaos = true;
/// <summary>
/// 是否输出燥点(默认输出)
/// </summary>
public bool Chaos
{
get { return chaos; }
set { chaos = value; }
}
Color chaosColor = Color.LightGray;
/// <summary>
/// 输出燥点的颜色(默认灰色)
/// </summary>
public Color ChaosColor
{
get { return chaosColor; }
set { chaosColor = value; }
}
Color backgroundColor = Color.White;
/// <summary>
/// 自定义背景色(默认白色)
/// </summary>
public Color BackgroundColor
{
get { return backgroundColor; }
set { backgroundColor = value; }
}
Color[] colors = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };
/// <summary>
/// 自定义随机颜色数组
/// </summary>
public Color[] Colors
{
get { return colors; }
set { colors = value; }
}
string[] fonts = { "Arial", "Georgia" };
/// <summary>
/// 自定义字体数组
/// </summary>
public string[] Fonts
{
get { return fonts; }
set { fonts = value; }
}
#region 产生波形滤镜效果
private const double PI = 3.1415926535897932384626433832795;
private const double PI2 = 6.283185307179586476925286766559;
/// <summary>
/// 正弦曲线Wave扭曲图片（Edit By 51aspx.com）
/// </summary>
/// <param name="srcBmp">图片路径</param>
/// <param name="bXDir">如果扭曲则选择为True</param>
/// <param name="nMultValue">波形的幅度倍数，越大扭曲的程度越高，一般为3</param>
/// <param name="dPhase">波形的起始相位，取值区间[0-2*PI)</param>
/// <returns></returns>
public System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
{
System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
// 将位图背景填充为白色
System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp);
graph.FillRectangle(new SolidBrush(System.Drawing.Color.White), 0, 0, destBmp.Width, destBmp.Height);
graph.Dispose();
double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
for (int i = 0; i < destBmp.Width; i++)
{
for (int j = 0; j < destBmp.Height; j++)
{
double dx = 0;
dx = bXDir ? (PI2 * (double)j) / dBaseAxisLen : (PI2 * (double)i) / dBaseAxisLen;
dx += dPhase;
double dy = Math.Sin(dx);
// 取得当前点的颜色
int nOldX = 0, nOldY = 0;
nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
nOldY = bXDir ? j : j + (int)(dy * dMultValue);
System.Drawing.Color color = srcBmp.GetPixel(i, j);
if (nOldX >= 0 && nOldX < destBmp.Width
&& nOldY >= 0 && nOldY < destBmp.Height)
{
destBmp.SetPixel(nOldX, nOldY, color);
}
}
}
return destBmp;
}
#endregion
/// <summary>
/// 生成校验码图片
/// </summary>
/// <param name="code">验证码</param>
/// <returns></returns>
public Bitmap CreateImage(string code)
{
int fSize = FontSize;
int fWidth = fSize + Padding;
int imageWidth = (int)(code.Length * fWidth) + 4 + Padding * 2;
int imageHeight = fSize * 2 + Padding * 2;
System.Drawing.Bitmap image = new System.Drawing.Bitmap(imageWidth, imageHeight);
Graphics g = Graphics.FromImage(image);
g.Clear(BackgroundColor);
//给背景添加随机生成的燥点
if (this.Chaos)
{
Pen pen = new Pen(ChaosColor, 0);
int c = Length * 10;
for (int i = 0; i < c; i++)
{
int x = rnd.Next(image.Width);
int y = rnd.Next(image.Height);
g.DrawRectangle(pen, x, y, 1, 1);
}
}
int left = 0, top = 0, top1 = 1, top2 = 1;
int n1 = (imageHeight - FontSize - Padding * 2);
int n2 = n1 / 4;
top1 = n2;
top2 = n2 * 2;
Font f;
Brush b;
int cindex, findex;
//随机字体和颜色的验证码字符
for (int i = 0; i < code.Length; i++)
{
cindex = rnd.Next(Colors.Length - 1);
findex = rnd.Next(Fonts.Length - 1);
f = new System.Drawing.Font(Fonts[findex], fSize, System.Drawing.FontStyle.Bold);
b = new System.Drawing.SolidBrush(Colors[cindex]);
if (i % 2 == 1)
{
top = top2;
}
else
{
top = top1;
}
left = i * fWidth;
g.DrawString(code.Substring(i, 1), f, b, left, top);
}
//画一个边框 边框颜色为Color.Gainsboro
g.DrawRectangle(new Pen(Color.Gainsboro, 0), 0, 0, image.Width - 1, image.Height - 1);
g.Dispose();
//产生波形（Add By 51aspx.com）
image = TwistImage(image, true, 8, 4);
return image;
}
/// <summary>
/// 生成随机字符码
/// </summary>
/// <param name="codeLen">字符串长度</param>
/// <param name="zhCharsCount">中文字符数</param>
/// <returns></returns>
public string CreateVerifyCode(int codeLen, int zhCharsCount)
{
char[] chs = new char[codeLen];
int index;
for (int i = 0; i < zhCharsCount; i++)
{
index = rnd.Next(0, codeLen);
if (chs[index] == '\0')
chs[index] = CreateZhChar();
else
--i;
}
for (int i = 0; i < codeLen; i++)
{
if (chs[i] == '\0')
chs[i] = CreateEnOrNumChar();
}
return new string(chs, 0, chs.Length);
}
/// <summary>
/// 生成默认长度5的随机字符码
/// </summary>
/// <returns></returns>
public string CreateVerifyCode()
{
return CreateVerifyCode(Length, 0);
}
/// <summary>
/// 生成英文或数字字符
/// </summary>
/// <returns></returns>
protected char CreateEnOrNumChar()
{
return EnglishOrNumChars[rnd.Next(0, EnglishOrNumChars.Length)];
}
/// <summary>
/// 生成汉字字符
/// </summary>
/// <returns></returns>
protected char CreateZhChar()
{
//若提供了汉字集，查询汉字集选取汉字
if (ChineseChars.Length > 0)
{
return ChineseChars[rnd.Next(0, ChineseChars.Length)];
}
//若没有提供汉字集，则根据《GB2312简体中文编码表》编码规则构造汉字
else
{
byte[] bytes = new byte[2];
//第一个字节值在0xb0, 0xf7之间
bytes[0] = (byte)rnd.Next(0xb0, 0xf8);
//第二个字节值在0xa1, 0xfe之间
bytes[1] = (byte)rnd.Next(0xa1, 0xff);
//根据汉字编码的字节数组解码出中文汉字
string str1 = Encoding.GetEncoding("gb2312").GetString(bytes);
return str1[0];
}
}
}
这里面大量使用了51aspx.com的代码，在此表示感谢。这里的主要改进在于支持生成中英文混合的验证码。中文的生成有两种方式，一是根据《GB2312简体中文编码表》编码规则构造汉字，二是从一个选定的中文字符集合中随即选取汉字。实现很简单，参考函数protected char CreateZhChar()，在此不赘述。
最后说一下验证码的使用，下面是一个例子：
<img src="VerifyCode.aspx" id="valiCode" alt="验证码" />
<a title="刷新验证码" href="#" onclick="javascript:document.getElementById('valiCode').src='VerifyCode.aspx?id='+Math.random();return false;">看不清，换张图片？</a>
<a title="刷新验证码" href="#" onclick="javascript:document.getElementById('valiCode').src='VerifyCode.aspx?id='+Math.random();return false;">看不清，换张图片？</a>
这里有个小技巧，就是在刷新验证码的使用，验证码的URL后面用了随机参数以欺骗浏览器重新请求。
源代码
2500常用汉字
498常用汉字