生成验证码原理：产生随机字符，并将字符生成为图片，同时储存到Session里去，然后验证用户输入的内容是否与Session中的验证码相符即可。
效果图：用户可以点击切换验证码信息。
一般处理程序：CheckCodeHandler.cs
<%@ WebHandler Language="C#" %> using System; using System.Web; using System.Text; using System.Drawing; using System.Web.SessionState; public class CheckCodeHandler : IHttpHandler,IRequiresSessionState { //产生验证码的字符集 public string charcode = "2,3,4,5,6,8,9,A,B,C,D,E,F,G,H,J,K,M,N,P,R,S,U,W,X,Y,a,b,c,d,e,f,g,h,j,k,m,n,p,r,s,u,w,x,y"; public void ProcessRequest (HttpContext context) { string validateCode = CreateRandomCode(4); context.Session["ValidateCode"] = validateCode;//将验证码保存到session中 CreateCodeImage(validateCode, context); } public bool IsReusable { get { return false; } } /// <summary> /// 生成验证码 /// </summary> /// <param>验证码个数</param> /// <returns>验证码字符串</returns> public string CreateRandomCode(int n) { string[] CharArray = charcode.Split(',');//将字符串转换为字符数组 string randomCode = ""; int temp = -1; Random rand = new Random(); for (int i = 0; i < n; i++) { if (temp != -1) { rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); } int t = rand.Next(CharArray.Length - 1); if (temp != -1 && temp == t) { return CreateRandomCode(n); } temp = t; randomCode += CharArray[t]; } return randomCode; } public void CreateCodeImage(string checkCode, HttpContext context) { int iwidth = (int)(checkCode.Length * 13); System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 20); Graphics g = Graphics.FromImage(image); Font f = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Italic | System.Drawing.FontStyle.Bold)); // 前景色 Brush b = new System.Drawing.SolidBrush(Color.Black); // 背景色 g.Clear(Color.White); // 填充文字 g.DrawString(checkCode, f, b, 0, 1); // 随机线条 Pen linePen = new Pen(Color.Gray, 0); Random rand = new Random(); for (int i = 0; i < 5; i++) { int x1 = rand.Next(image.Width); int y1 = rand.Next(image.Height); int x2 = rand.Next(image.Width); int y2 = rand.Next(image.Height); g.DrawLine(linePen, x1, y1, x2, y2); } // 随机点 for (int i = 0; i < 30; i++) { int x = rand.Next(image.Width); int y = rand.Next(image.Height); image.SetPixel(x, y, Color.Gray); } // 边框 g.DrawRectangle(new Pen(Color.Gray), 0, 0, image.Width - 1, image.Height - 1); // 输出图片 System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); context.Response.ClearContent(); context.Response.ContentType = "image/jpeg"; context.Response.BinaryWrite(ms.ToArray()); g.Dispose(); image.Dispose(); } }
封装成类库：ValidateNumber.cs
using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Drawing; using System.Web.UI; using System.Drawing.Drawing2D; using System.IO; using System.Drawing.Imaging; /// <summary> ///ValidateNumber 生成验证码 /// </summary> public class ValidateNumber { //产生验证码的字符集 （易混淆的字符去掉） private string charcode = "2,3,4,5,6,8,9,A,B,C,D,E,F,G,H,J,K,M,N,P,R,S,U,W,X,Y,a,b,c,d,e,f,g,h,j,k,m,n,p,r,s,u,w,x,y"; /// <summary> /// 验证码的最大长度 /// </summary> public int MaxLength { get { return 10; } } /// <summary> /// 验证码的最小长度 /// </summary> public int MinLength { get { return 1; } } /// <summary> /// 生成验证码 /// </summary> /// <param>指定验证码的长度</param> /// <returns></returns> public string CreateValidateNumber(int length) { string[] CharArray = charcode.Split(',');//将字符串转换为字符数组 string randomCode = ""; int temp = -1; Random rand = new Random(); for (int i = 0; i < length; i++) { if (temp != -1) { rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); } int t = rand.Next(CharArray.Length - 1); if (temp != -1 && temp == t) { return CreateValidateNumber(length); } temp = t; randomCode += CharArray[t]; } return randomCode; } /// <summary> /// 创建验证码的图片 /// </summary> /// <param>context对象</param> /// <param>验证码</param> public void CreateValidateGraphic(HttpContext context,string validateNum) { int iwidth = (int)(validateNum.Length * 14); Bitmap image = new Bitmap(iwidth, 22); Graphics g = Graphics.FromImage(image); try { //生成随机生成器 Random random = new Random(); //清空图片背景色 g.Clear(Color.White); //画图片的干扰线 for (int i = 0; i < 25; i++) { int x1 = random.Next(image.Width); int x2 = random.Next(image.Width); int y1 = random.Next(image.Height); int y2 = random.Next(image.Height); g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2); } Font font = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic)); LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true); g.DrawString(validateNum, font, brush, 3, 2); //画图片的前景干扰点 for (int i = 0; i < 100; i++) { int x = random.Next(image.Width); int y = random.Next(image.Height); image.SetPixel(x, y, Color.FromArgb(random.Next())); } //画图片的边框线 g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); //保存图片数据 MemoryStream stream = new MemoryStream(); image.Save(stream, ImageFormat.Jpeg); //输出图片 context.Response.Clear(); context.Response.ContentType = "image/jpeg"; context.Response.BinaryWrite(stream.ToArray()); } finally { g.Dispose(); image.Dispose(); } } /// <summary> /// 得到验证码图片的长度 /// </summary> /// <param>验证码的长度</param> /// <returns></returns> public static int GetImageWidth(int validateNumLength) { return (int)(validateNumLength * 14); } /// <summary> /// 得到验证码图片的高度 /// </summary> /// <returns></returns> public static double GetImageHeight() { return 22; } }