现在很多网站都有注册登录的页面，为了更好的满足用户体验和网站的安全性，很多网站都采用动态生成的图形码或者是附加码进行验证,下面把生成验证码的方法给大家整理如下.

实现验证技术就是在服务器端生成一个随机数，并将其保存在内存中，发送给浏览器，并以图片的形式提交给用户。之前在做项目过程中，完成了一个利用script进行用户注册及登录的验证码时，发现有各种生成验证码的方式，下面主要是几种不同的生成验证码的方式：

1、绘制纯数字的网站验证码

本实例实现的是数字验证码技术，即随机生成4位数字作为验证码。在开发绘制会员登录验证模块时可以使用数字验证码技术。

■设计过程

在一个新建的窗体CheckCode.aspx中编写生成数字验证码的方法：

private string RndNum() { int number; char code; string checkCode = String.Empty; System.Random random = new Random(); for (int i = 0; i < 4; i++) { number = random.Next(); if (number % 2 == 0) code = (char)('0' + (char)(number % 10)); else code = (char)('A' + (char)(number % 26)); checkCode += code.ToString(); } Response.Cookies.Add(new HttpCookie("yzmcode", 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)), 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); //画图片的背景噪音线 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 System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic)); 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); //画图片的前景噪音点 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); System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); Response.ClearContent(); Response.ContentType = "image/Gif"; Response.BinaryWrite(ms.ToArray()); } finally { g.Dispose(); image.Dispose(); } }

然后在Page_Load中调用CreateCheckCodeImage（）：

protected void Page_Load(object sender, EventArgs e) { this.CreateCheckCodeImage(RndNum()); }那么在我们登录的窗口中就可以通过简单的控件：<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <asp:ImageButton ID="ImageButton2" runat="server" ImageUrl="~/CheckCode.aspx" Width="50" Height="30"/><asp:Label ID="Label1" runat="server" Text="看不清楚？点击图片换一个" Height="16px" Font-Size="Small" ForeColor="Red"></asp:Label> <br /> <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />在Button1_Click中对验证码输入的正确性进行判断：protected void Button1_Click(object sender, EventArgs e){ if (String.Compare(Request.Cookies["yzmcode"].Value, TextBox1.Text, true) != 0) { Response.Write("<script>alert('验证码错误！')</script>"); } else Response.Write("<script>alert('验证码正确！')</script>");}

2、绘制数字与字母组合的网站验证码

和纯数字的很相似，具体区别在随机生成字符串的方法中

private string GenerateCheckCode() { int number; char code; string checkCode = String.Empty; Random random = new Random(); for (int i = 0; i < 4; i++) { number = random.Next(); if (number % 2 == 0) code = (char)('0' + (char)(number % 10)); else code = (char)('A' + (char)(number % 26)); checkCode += code.ToString(); } Response.Cookies.Add(new HttpCookie("CheckCode", checkCode)); return checkCode; }

字符串生成后，接下来就是将该字符串绘制成图片显示出来。代码如下：

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)), 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); //画图片的背景噪音线 for (int i = 0; i < 2; 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.Black), x1, y1, x2, y2); } Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold)); 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); //画图片的前景噪音点 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); System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif); Response.ClearContent(); Response.ContentType = "image/Gif"; Response.BinaryWrite(ms.ToArray()); } finally { g.Dispose(); image.Dispose(); } }

在登录的窗口进行验证码输入是否正确的判断：

protected void Button1_Click(object sender, EventArgs e) { HttpCookie cookie = Request.Cookies["CheckCode"]; if (cookie.Value == this.TextBox1.Text.Trim()) { Response.Write("<script>alert('验证码正确！')</script>"); } else { Response.Write("<script>alert('验证码错误！')</script>"); } }

那么有关于数字与字母组合的网站验证码就生成了。

3、四则运算式的验证码

其他的和数字和字母混合生成的验证码相似，我就不写了，具体区别在随机生成四则运算式的方法中，如下：

private string GenerateCheckCode() { Random rd = new Random(); int Results = 0; int Num1 = rd.Next(10); int Num2 = rd.Next(10); string Expressions = ""; int F = (rd.Next(4) + 1); switch (F) { case 1: Results = Num1 + Num2; Expressions = Num1 + "+" + Num2; break; case 2: Results = Num1 - Num2; Expressions = Num1 + "-" + Num2; break; case 3: Results = Num1 * Num2; Expressions = Num1 + "*" + Num2; break; case 4: if (Num2 > 0) { Results = Convert.ToInt16(Num1 / Num2); Expressions = Num1 + "/" + Num2; } else { Results = Num1; Expressions = Num1 + "/1"; } break; } Session["Code"] = Results.ToString(); return Expressions;}

此篇文章主要介绍了三种方法生成验证码，希望大家喜欢。