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 _Default : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { CreateCheckCodeImage(GenerateCheckCode()); } } // 产生四位随机数的方法 private string GenerateCheckCode() { int number; char code; //表示字符串为空，次字段为只读 string checkCode = string.Empty; Random random = new Random(); for (int i = 0; i < 4; i++) { number = random.Next(); code = (char)('0' + (char)(number % 10)); checkCode += code.ToString(); } //将验证码保存到cookie中 Response.Cookies.Add(new HttpCookie("CheckCode", checkCode)); return checkCode; } private void CreateCheckCodeImage(string checkCode) { //当随机数是空的时候或者 去掉空格还是空的时候 if (checkCode == null || checkCode.Trim() == string.Empty) return; // 创建位图 4 * 12.5 System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 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); //画图片的毕竟噪音线 for (int i = 0; i < 2; i++) { //产生随机的起始坐标和重点坐标 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.Black), x1, y1, x2, y2); } //字体 大小12 加粗 Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold)); // 线性渐变封装 System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true); g.DrawString(checkCode, font, brush, 2, 2); // 画图片的前景噪点 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())); } // 花图片的边框线 矩形 g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); //创建其支持存储区为内存的 System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); // 清楚缓冲区流中的所有内容输出 Response.ClearContent(); // 获取或设置输出流的格式 Response.ContentType = "image/gif"; //将一个二进制字符串 写入输出流 ms.ToArray()将整个流内容写入数组 Response.BinaryWrite(ms.ToArray()); } finally { // 释放资源 g.Dispose(); image.Dispose(); } }} 展示的页面： 验证码用HTML标签ima表示的 src的路径制定到Code.aspx 当点击图片的时候自动的刷新图片的路径 达到更换验证码的目的.。是通过js刷新img的src的路径实现的 <img id="Img1" alt="看不清，请点击我！" οnclick="this.src=this.src+'?'" src="Code.aspx" style="width: 73px; height: 22px" align="left" />验证页面的后台代码：
protected void Button1_Click( object sender, EventArgs e) { string code = this.txtCode.Text; // 从cookie中取出验证码 HttpCookie cookie = Request.Cookies[ " CheckCode "]; if (code == cookie.Value.ToString()) { Response.Write( " 正确 "); } else { Response.Write( " 错误 "); } }