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// RandomImage.aspx.cs驗證碼生成頁面后臺

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

        //隨機數種子
        Random random = new Random();

        for (int i = 0; i < 4; i++) //校驗碼長度為4
        {
            //隨機的整數
            number = random.Next();

            //字符從0-9,A-Z中隨機產生,對應的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中保存校驗碼
        Session["CheckCode"] = strCode;
        return strCode;
    }

    /// <summary>
    /// 根據校驗碼輸出圖片
    /// </summary>
    /// <param name="checkCode">產生的隨機校驗碼</param>
    private void CreateCheckCodeImage(string checkCode)
    {
        //若校驗碼為空，則直接返回
        if (checkCode == null || checkCode.Trim() == String.Empty)
        {
            return;
        }
        //根據校驗碼的長度確定輸出圖片的長度
        System.Drawing.Bitmap image = new System.Drawing.Bitmap(55, 20);//(int)Math.Ceiling(Convert.ToDouble(checkCode.Length * 15))
        //創(chuàng)建Graphics對象
        Graphics g = Graphics.FromImage(image);
        try
        {
            //生成隨機數種子
            Random random = new Random();
            //清空圖片背景色
            g.Clear(Color.White);
            //畫圖片的背景噪音線 10條
            //---------------------------------------------------
            for (int i = 0; i < 10; i++)
            {
                //噪音線起點坐標(x1,y1),終點坐標(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------------------------------
            //輸出圖片中校驗碼的字體: 12號Arial,粗斜體
            Font font = new Font("Arial",12,(FontStyle.Bold | FontStyle.Italic));

            //線性漸變畫刷
            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);

            //畫圖片的前景噪音點 50個
            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()));
            }

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

            //創(chuàng)建內存流用于輸出圖片
            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類型設置為"image/Png"
                Response.ContentType = "image/Jpeg";
                //輸出圖片的二進制流
                Response.BinaryWrite(ms.ToArray());
            }
        }
        finally
        {
            //釋放Bitmap對象和Graphics對象
            g.Dispose();
            image.Dispose();
        }
    }
}
//--------------------------------------------------------------------

//測試頁面 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" "