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.Drawing.Drawing2D;

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

        GetCheckCodeImage(GetCode(5));
    }
    //产生随机字符串 
    private string GetCode(int num)
    {
        string[] source ={ "1", "2", "3", "4", "5", "6", "7", "8", "9", "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", 
            "K", "L", "M", "N", "O","P", "Q", "R", "S", "T", "U", "V", "W", "X", "Y", "Z" ,"a", "b", "c", "d", "e", "f", "g", "h", "i", "j", 
            "k", "l", "m", "n", "o", "p", "q", "r", "s", "t", "u", "v", "w", "x", "y","z"};
        string code = "";
        Random rd = new Random();
        for (int i = 0; i < num; i++)
        {
            
            code += source[rd.Next(0, source.Length)];
        }
        Session["ValidateCode"] = code;//将字符串保存到Session中，以便需要时进行验证  
        return code;

    }


    #region    验证码
    /// <summary>
    /// 生成验证码
    /// </summary>
    /// <param name="checkCode"></param>
    private void GetCheckCodeImage(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)), 18);
        Graphics g = Graphics.FromImage(image);
        try
        {
            Random random = new Random();     //生成随机生成器 
            g.Clear(Color.White);            //清空图片背景色
            for (int i = 0; i < 5; i++)     //画图片的背景噪音线
            {
                int x1 = random.Next(image.Width);
                int x2 = random.Next(image.Width);
                int y1 = random.Next(image.Height);
                int y2 = random.Next(image.Height);
                if (i / 2 == 0)
                {
                    g.DrawLine(new Pen(Color.Red), x1, y1, x2, y2);
                }
                else
                {
                    g.DrawLine(new Pen(Color.Blue), x1, y1, x2, y2);
                }
            }
            Font font = new System.Drawing.Font("Arial", 12, (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
            LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue,