現在很多網站都有注冊登錄的頁面，為了更好的滿足用戶體驗和網站的安全性，很多網站都采用動態生成的圖形碼或者是附加碼進行驗證,下面把生成驗證碼的方法給大家整理如下.
實現驗證技術就是在服務器端生成一個隨機數，并將其保存在內存中，發送給瀏覽器，并以圖片的形式提交給用戶。之前在做項目過程中，完成了一個利用script進行用戶注冊及登錄的驗證碼時，發現有各種生成驗證碼的方式，下面主要是幾種不同的生成驗證碼的方式：
1、繪制純數字的網站驗證碼
本實例實現的是數字驗證碼技術，即隨機生成4位數字作為驗證碼。在開發繪制會員登錄驗證模塊時可以使用數字驗證碼技術。
■設計過程
在一個新建的窗體CheckCode.aspx中編寫生成數字驗證碼的方法：
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 { //生成隨機生成器 Random random = new Random(); //清空圖片背景色 g.Clear(Color.White); //畫圖片的背景噪音線 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); //畫圖片的前景噪音點 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())); } //畫圖片的邊框線 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中調用CreateCheckCodeImage（）：
protected void Page_Load(object sender, EventArgs e) { this.CreateCheckCodeImage(RndNum()); }那么在我們登錄的窗口中就可以通過簡單的控件：<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？點擊圖片換一個" Height="16px" Font-Size="Small" ForeColor="Red"></asp:Label> <br /> <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" />在Button1_Click中對驗證碼輸入的正確性進行判斷：protected void Button1_Click(object sender, EventArgs e){ if (String.Compare(Request.Cookies["yzmcode"].Value, TextBox1.Text, true) != 0) { Response.Write("<script>alert('驗證碼錯誤！')</script>"); } else Response.Write("<script>alert('驗證碼正確！')</script>");}2、繪制數字與字母組合的網站驗證碼
和純數字的很相似，具體區別在隨機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，接下來就是將該字符串繪制成圖片顯示出來。代碼如下：
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 { //生成隨機生成器 Random random = new Random(); //清空圖片背景色 g.Clear(Color.White); //畫圖片的背景噪音線 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); //畫圖片的前景噪音點 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())); } //畫圖片的邊框線 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(); } } 在登錄的窗口進行驗證碼輸入是否正確的判斷：
protected void Button1_Click(object sender, EventArgs e) { HttpCookie cookie = Request.Cookies["CheckCode"]; if (cookie.Value == this.TextBox1.Text.Trim()) { Response.Write("<script>alert('驗證碼正確！')</script>"); } else { Response.Write("<script>alert('驗證碼錯誤！')</script>"); } }那么有關于數字與字母組合的網站驗證碼就生成了。
3、四則運算式的驗證碼
其他的和數字和字母混合生成的驗證碼相似，我就不寫了，具體區別在隨機生成四則運算式的方法中，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;}
此篇文章主要介紹了三種方法生成驗證碼，希望大家喜歡。
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