本文實例講述了ASP.NET生成圖形驗證碼的方法。分享給大家供大家參考，具體如下：
通常生成一個圖形驗證碼主要 有3個步驟：
（1）隨機產(chǎn)生一個長度為N的隨機字符串，N的值可由開發(fā)可由開發(fā)人員自行設(shè)置。該字符串可以包含數(shù)字、字母等。
（2）將隨機生成的字符串創(chuàng)建成圖片，并顯示。
（3）保存驗證碼。
新建一個頁面為default.aspx, 放置一個TextBox控件和一個Image控件，TextBox控件用于輸入生成的字符串，Image控件用于顯示字符串，它的圖片就為生成的圖形驗證碼imageUrl=“/default.aspx”；
default.aspx頁面的源代碼為：
<form id="form1" runat="server"> <div> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <asp:Image ID="Image1" imageUrl=“/default.aspx” runat="server" /> </div></form>
圖形驗證碼的代碼為：
using System;using System.Configuration;using System.Data;using System.Linq;using System.Web;using System.Web.Security;using System.Web.UI;using System.Web.UI.HtmlControls;using System.Web.UI.WebControls;using System.Web.UI.WebControls.WebParts;using System.Xml.Linq;using System.Drawing;public partial class _Default : System.Web.UI.Page { protected void Page_Load(object sender, EventArgs e) { if (!IsPostBack) { string validateNum = CreateRandomNum(4); CreateImage(validateNum); Session["ValidateNum"] = validateNum; } } //生產(chǎn)隨機數(shù) private string CreateRandomNum(int NumCount) { string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,O,P,Q,R,S,T,U,W,X,Y,Z,a,b,c,d,e,f,g,h,i,j,k,m,n,o,p,q,s,t,u,w,x,y,z"; string[] allCharArray = allChar.Split(',');//拆分成數(shù)組 string randomNum = ""; int temp = -1; //記錄上次隨機數(shù)的數(shù)值，盡量避免產(chǎn)生幾個相同的隨機數(shù) Random rand = new Random(); for (int i = 0; i < NumCount; i++) { if (temp != -1) { rand = new Random(i*temp*((int)DateTime.Now.Ticks)); } int t = rand.Next(35); if (temp == t) { return CreateRandomNum(NumCount); } temp = t; randomNum += allCharArray[t]; } return randomNum; } //生產(chǎn)圖片 private void CreateImage(string validateNum) { if (validateNum == null || validateNum.Trim() == string.Empty) return; //生成BitMap圖像 System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length*12+12,22); Graphics g = Graphics.FromImage(image); try { //生成隨機生成器 Random random = new Random(); //清空圖片背景 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,x2,y1,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(validateNum,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(); //將圖像保存到指定流 image.Save(ms,System.Drawing.Imaging.ImageFormat.Gif); Response.ClearContent(); Response.ContentType="image/Gif"; Response.BinaryWrite(ms.ToArray()); } finally { g.Dispose(); image.Dispose(); } }} 
