小教室:驗證碼的功能:
幾年前,網站、論壇之類的大部分是沒有驗證碼的,因為一般使用者來說驗證碼只是增加了使用者的操作,降低了使用者的體驗。但後來各種灌水機器人、投票機器人、惡意註冊機器人層出不窮,大大增加了網站的負擔同時也為網站資料庫帶來了大量的垃圾資料。為了防止各種機器人程式的破壞,於是程式設計師想出了只有人眼能夠辨識的,程式不容易辨識的驗證碼!
驗證碼是一張圖片,將字母、數字甚至漢字作為圖片的內容,這樣一張圖片中的內容用人眼很容易識別,而程式將無法識別。在進行資料庫操作之前(例如登入驗證、投票、發佈、回覆、註冊等等)程序先驗證用戶端提交的驗證碼是否與圖片中的內容相同,如果相同則進行資料庫操作,則不同則提示驗證碼錯誤,不進行資料庫操作。這樣各種機器人程式就被拒於門外了!
但是隨著電腦科學的發展,模式識別等技術越來越成熟,於是編寫機器人程式的傢伙可以透過程式將直接寫在圖片中的內容識別出來,然後提交到伺服器,這樣驗證碼將形同虛設。為了防止機器人程式的識別,驗證碼的圖片產生也不斷在發展,加入乾擾點、幹擾線,文字變形、變換角度位置,顏色不同…各種防止電腦辨識的技術也應用到驗證碼中。就在這兩種技術的競爭中,於是便形成了我們現在看到的驗證碼,已經有很多人在抱怨“這是什麼驗證碼哦,人眼都分辨不清楚是什麼”,一切也是無奈。
了解了驗證碼的作用,下面寫一個簡單的驗證碼生成及使用的實例
先建個頁面用來展示驗證碼和判斷驗證碼輸入是否正確
<html xmlns="http://www.w3.org/1999/xhtml"> <head runat="server"> <title></title> <script src="Scripts/jquery-1.4.1.min.js" type="text/javascript"></script> <script type="text/javascript"> //点击切换验证码 function f_refreshtype() { var Image1 = document.getElementById("img"); if (Image1 != null) { Image1.src = Image1.src + "?"; } } </script> </head> <body> <form id="form1" runat="server"> <div> <table> <tr> <td> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> </td> <td> <img src="png.aspx" id="img" onclick="f_refreshtype()" / alt=".net驗證碼產生及使用方法" > </td> <td> <asp:Button ID="Button1" runat="server" Text="确定" /> </td> </tr> </table> </div> </form> </body> </html>
此頁後台對驗證碼進行驗證
protected void Page_Load(object sender, EventArgs e) { //生成的验证码被保存到session中 if (Session["CheckCode"] != null) { string checkcode = Session["CheckCode"].ToString(); if (this.TextBox1.Text == checkcode) { ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('验证码输入正确!')", true); } else { ClientScript.RegisterClientScriptBlock(this.GetType(), "", "alert('验证码输入错误!')", true); } } }
產生驗證碼頁面png.aspx
protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { CreateCheckCodeImage(GenerateCheckCodes(4)); } } public void ShowAuthCode(Stream stream, out string code) { Random random = new Random(); code = random.Next(1000, 9999).ToString(); Bitmap bitmap = CreateAuthCode(code); bitmap.Save(stream, System.Drawing.Imaging.ImageFormat.Gif); } private string GenerateCheckCodes(int iCount) { int number; string checkCode = String.Empty; int iSeed = DateTime.Now.Millisecond; System.Random random = new Random(iSeed); for (int i = 0; i < iCount; i++) { number = random.Next(10); checkCode += number.ToString(); } Session["CheckCode"] = checkCode; return checkCode; } private Bitmap CreateAuthCode(string str) { Font fn = new Font("宋体", 12); Brush forecolor = Brushes.Black; Brush bgcolor = Brushes.White; PointF pf = new PointF(5, 5); Bitmap bitmap = new Bitmap(100, 25); Rectangle rec = new Rectangle(0, 0, 100, 25); Graphics gh = Graphics.FromImage(bitmap); gh.FillRectangle(bgcolor, rec); gh.DrawString(str, fn, forecolor, pf); return bitmap; } private void CreateCheckCodeImage(string checkCode) { if (checkCode == null || checkCode.Trim() == String.Empty) return; int iWordWidth = 15; int iImageWidth = checkCode.Length * iWordWidth; Bitmap image = new Bitmap(iImageWidth, 20); 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); //画图片的背景噪音点 for (int i = 0; i < 20; 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); } //画图片的背景噪音线 for (int i = 0; i < 2; i++) { int x1 = 0; int x2 = image.Width; int y1 = random.Next(image.Height); int y2 = random.Next(image.Height); if (i == 0) { g.DrawLine(new Pen(Color.Gray, 2), x1, y1, x2, y2); } } for (int i = 0; i < checkCode.Length; i++) { string Code = checkCode[i].ToString(); int xLeft = iWordWidth * (i); random = new Random(xLeft); int iSeed = DateTime.Now.Millisecond; int iValue = random.Next(iSeed) % 4; if (iValue == 0) { Font font = new Font("Arial", 13, (FontStyle.Bold | System.Drawing.FontStyle.Italic)); Rectangle rc = new Rectangle(xLeft, 0, iWordWidth, image.Height); LinearGradientBrush brush = new LinearGradientBrush(rc, Color.Blue, Color.Red, 1.5f, true); g.DrawString(Code, font, brush, xLeft, 2); } else if (iValue == 1) { Font font = new System.Drawing.Font("楷体", 13, (FontStyle.Bold)); Rectangle rc = new Rectangle(xLeft, 0, iWordWidth, image.Height); LinearGradientBrush brush = new LinearGradientBrush(rc, Color.Blue, Color.DarkRed, 1.3f, true); g.DrawString(Code, font, brush, xLeft, 2); } else if (iValue == 2) { Font font = new System.Drawing.Font("宋体", 13, (System.Drawing.FontStyle.Bold)); Rectangle rc = new Rectangle(xLeft, 0, iWordWidth, image.Height); LinearGradientBrush brush = new LinearGradientBrush(rc, Color.Green, Color.Blue, 1.2f, true); g.DrawString(Code, font, brush, xLeft, 2); } else if (iValue == 3) { Font font = new System.Drawing.Font("黑体", 13, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Bold)); Rectangle rc = new Rectangle(xLeft, 0, iWordWidth, image.Height); LinearGradientBrush brush = new LinearGradientBrush(rc, Color.Blue, Color.Green, 1.8f, true); g.DrawString(Code, font, brush, xLeft, 2); } } //////画图片的前景噪音点 //for (int i = 0; i < 8; 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.BinaryWrite(ms.ToArray()); } finally { g.Dispose(); image.Dispose(); } }
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