//---------------------------------------------

// RandomImage.aspx.cs驗(yàn)證碼生成頁(yè)面后臺(tái)

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;
using System.IO;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.Drawing.Printing;

public partial class RandomImage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

        CreateCheckCodeImage(GenerateCheckCode());
    }
    /// <summary>
    /// 生成隨機(jī)校驗(yàn)碼字符串
    /// </summary>
    /// <returns>生成的隨機(jī)校驗(yàn)碼字符串</returns>
    private string GenerateCheckCode()
    {
        int number;
        string strCode = string.Empty;

        //隨機(jī)數(shù)種子
        Random random = new Random();

        for (int i = 0; i < 4; i++) //校驗(yàn)碼長(zhǎng)度為4
        {
            //隨機(jī)的整數(shù)
            number = random.Next();

            //字符從0-9,A-Z中隨機(jī)產(chǎn)生,對(duì)應(yīng)的ASCII碼分別為
            //48-57,65-90
            number = number % 36;
            if (number < 10)
            {
                number += 48;
            }
            else
            {
                number += 55;
            }
            strCode += ((char)number).ToString();
        }

        //在session中保存校驗(yàn)碼
        Session["CheckCode"] = strCode;
        return strCode;
    }

    /// <summary>
    /// 根據(jù)校驗(yàn)碼輸出圖片
    /// </summary>
    /// <param name="checkCode">產(chǎn)生的隨機(jī)校驗(yàn)碼</param>
    private void CreateCheckCodeImage(string checkCode)
    {
        //若校驗(yàn)碼為空，則直接返回
        if (checkCode == null || checkCode.Trim() == String.Empty)
        {
            return;
        }
        //根據(jù)校驗(yàn)碼的長(zhǎng)度確定輸出圖片的長(zhǎng)度
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(55, 20);//(int)Math.Ceiling(Convert.ToDouble(checkCode.Length * 15))
        //創(chuàng)建Graphics對(duì)象
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成隨機(jī)數(shù)種子
            Random random = new Random();
            //清空?qǐng)D片背景色
            g.Clear(Color.White);
            //畫(huà)圖片的背景噪音線 10條
            //---------------------------------------------------
            for (int i = 0; i < 10; i++)
            {
                //噪音線起點(diǎn)坐標(biāo)(x1,y1),終點(diǎn)坐標(biāo)(x2,y2)
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);

                //用銀色畫(huà)出噪音線
                g.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2);
            }
            //---------------------------------------------------
            //Brush b = Brushes.Silver;
            //g.FillRectangle(b, 0, 0, image.Width, image.Height);
            //---------------------以上兩種任選其一------------------------------
            //輸出圖片中校驗(yàn)碼的字體: 12號(hào)Arial,粗斜體
            Font font = new Font("Arial",12,(FontStyle.Bold | FontStyle.Italic));

            //線性漸變畫(huà)刷
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height),Color.Blue,Color.Purple,1.2f,true);
            g.DrawString(checkCode, font, brush, 2, 2);

            //畫(huà)圖片的前景噪音點(diǎn) 50個(gè)
            for (int i = 0; i < 50; i++)
            {
                int x = random.Next(image.Width);
                int y = random.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(random.Next()));
            }

            //畫(huà)圖片的邊框線
            g.DrawRectangle(new Pen(Color.Peru),0,0,image.Width - 1,image.Height - 1);

            //創(chuàng)建內(nèi)存流用于輸出圖片
            using (MemoryStream ms = new MemoryStream())
            {
                //圖片格式指定為png
                image.Save(ms, ImageFormat.Jpeg);
                //清除緩沖區(qū)流中的所有輸出
                Response.ClearContent();
                //輸出流的HTTP MIME類型設(shè)置為"image/Png"
                Response.ContentType = "image/Jpeg";
                //輸出圖片的二進(jìn)制流
                Response.BinaryWrite(ms.ToArray());
            }
        }
        finally
        {
            //釋放Bitmap對(duì)象和Graphics對(duì)象
            g.Dispose();
            image.Dispose();
        }
    }
}
//--------------------------------------------------------------------

//測(cè)試頁(yè)面 dafault.aspx

<%@ Page Language="C#" AutoEventWireup="true"  CodeFile="Default.aspx.cs" Inherits="_Default" Debug="true" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www./TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www./1999/xhtml">
<head runat="server">
    <title>無(wú)標(biāo)題頁(yè)</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    <asp:TextBox ID="txtCode" runat="server"></asp:TextBox>
        <asp:Image ID="Image1" runat="server" ImageUrl="~/RandomImage.aspx" />
        <asp:Button ID="Button1" runat="server" onclick="Button1_Click" Text="Button" /><hr />
        <asp:Label ID="lblMsg" runat="server" Text="Label"></asp:Label>
    </div>
    </form>
</body>
</html>
//----------------------------------------------------

//測(cè)試頁(yè)面后臺(tái)

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;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        if (string.Compare(Session["CheckCode"].ToString(), this.txtCode.Text, true) != 0)
        {
            lblMsg.Text = "驗(yàn)證碼錯(cuò)誤，請(qǐng)輸入正確的驗(yàn)證碼。";
            return;
        }
        else
        {
            lblMsg.Text = "成功";
        }
    }
}

本文來(lái)自CSDN博客，轉(zhuǎn)載請(qǐng)標(biāo)明出處：http://blog.csdn.net/dhping/archive/2009/06/11/4261761.aspx