1、创建一个一般处理文件(后缀ashx)或者aspx页面也可以，建议是一般处理程序，因为aspx页面要经过一个页面生命周期，性能相对来说差一点，如果是小网站那就无关紧要了。
2、将输出格式更改为：image/JPEG(或image/png等等)，如果是一般处理程序请将你的类实现IRequiresSessionState这个接口，这个很重要，如果不实现的话，你的验证码无法通过session传递到站点。
3、接下来是页面代码部分：string[] str = new string[4];string ServerCode = "";string[] a = new string[62] { "0", "1", "2", "3", "4", "5", "6", "7", "8", "9", "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", "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" };Random random = new Random();for (int i = 0; i < 4; i++){int rd = random.Next(62);str[i] = a[rd];}string strs = "";foreach (string s in str){strs = strs + s;}ServerCode = strs;Session["ServerCode"] = ServerCode.ToLower();using (Bitmap bitmap = new Bitmap(70, 24)){using (Graphics g = Graphics.FromImage(bitmap)){g.Clear(Color.White);for (int i = 0; i < 10; i++){int x1=random.Next(bitmap.Width);int x2=random.Next(bitmap.Height);int x3=random.Next(bitmap.Width);int x4=random.Next(bitmap.Height);g.DrawLine(new Pen(Color.Silver), x1, x2, x3, x4);}for (int i = 0; i < 70; i++){int i1=random.Next(bitmap.Width);int i2=random.Next(bitmap.Height);bitmap.SetPixel(i1,i2,Color.FromArgb(random.Next()));}Point p1=new Point(0,0);Point p2=new Point(75,24);g.DrawString(ServerCode, new Font("宋体",16,FontStyle.Italic), new LinearGradientBrush(p1,p2,Color.OrangeRed,Color.Blue), new PointF(8, 0));g.DrawRectangle(new Pen(Color.DarkSeaGreen), 0, 0, bitmap.Width - 1, bitmap.Height - 1);}bitmap.Save(Response.OutputStream,System.Drawing.Imaging.ImageFormat.Jpeg);}在页面中写入如下代码测试：string ServerCode = Convert.ToString(Session["ServerCode"]);if (ServerCode == txtCheak.Text){Response.Write("正确");}else{Response.Write("错误");}到此详细介绍了验证码的创建，您可以根据您的业务需求来修改您的验证码
