C#生成随机验证码例子：

前端：

  <tr>

           <td width="24%" height="" align="center" valign="top">

               验证码：</td>

           <td valign="top" width="37%" align="left">

              <input type="text" name="txtCode" id="txtvalidateCode"/><a href="javascript:void(0)" id="valiateCode"><img src="/ashx/ValidateCode.ashx?id=1" id="imgCode" /></a><span style="font-size:14px;color:red " id="userCodeMsg"></span></td>

         </tr>

给验证码图片绑定单击事件：

 $("#valiateCode").click(function () {

  　　$("#imgCode").attr("src",$("#imgCode").attr("src")+1);

 });

后台生成验证码图片代码：

ValidateCode.ashx

 <%@ WebHandler Language="C#" Class="ValidateCode" %>

 using System;

 using System.Web;

 using System.Drawing;

 using System.Web.SessionState;

 public class ValidateCode : IHttpHandler, IRequiresSessionState

 {

     HttpContext context;

     public void ProcessRequest (HttpContext context1) {

         this.context = context1;

         CreateCheckCodeImage(GenerateCheckCode());

     }

     private string GenerateCheckCode()

     {

         int number;

         char code;

         string checkCode = String.Empty;

         System.Random random = new Random();

         for (int i = ; i < ; i++)

         {

             number = random.Next();

             if (number %  == )

                 code = (char)('' + (char)(number % ));

             else

                 code = (char)('' + (char)(number % ));

             //code = (char)('A' + (char)(number % 26));

             checkCode += code.ToString();

         }

         //添加Session值

         context.Session.Add("vCode", checkCode);

         return checkCode;

     }

     private void CreateCheckCodeImage(string checkCode)

     {

         if (checkCode == null || checkCode.Trim() == String.Empty)

             return;

         System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), );

         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);

             //画图片的背景噪音线

             for (int i = ; i < ; 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 System.Drawing.Font("Arial", , (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));

             System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(, , image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);

             g.DrawString(checkCode, font, brush, , );

             //画图片的前景噪音点

             for (int i = ; i < ; 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), , , image.Width - , image.Height - );

             System.IO.MemoryStream ms = new System.IO.MemoryStream();

             image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

             context.Response.ClearContent();

             context.Response.ContentType = "image/Gif";

             context.Response.BinaryWrite(ms.ToArray());

         }

         finally

         {

             g.Dispose();

             image.Dispose();

         }

     }

     public bool IsReusable {

         get {

             return false;

         }

     }

 }

验证码效果：

C#生成随机验证吗例子的相关教程结束。