第三种/WebForm1.aspx.cs

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using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;

namespace 验证码.第三种
{
    public partial class WebForm1 : System.Web.UI.Page
    {
        protected void Page_Load(object sender, EventArgs e)
        {
            this.CreateCheckCodeImage(RndNum()); 
        }
        private string RndNum()
        {
            int number;
            char code;
            string checkCode = String.Empty;

            System.Random random = new Random();

            for (int i = 0; i < 4; i++)
            {
                number = random.Next();
                if (number % 2 == 0)
                    code = (char)('0' + (char)(number % 10));
                else
                    code = (char)('A' + (char)(number % 26));
                checkCode += code.ToString();
            }
            Response.Cookies.Add(new HttpCookie("yzmcode", checkCode));
            return checkCode;
        }
        private void CreateCheckCodeImage(string checkCode)
        {
            if (checkCode == null || checkCode.Trim() == String.Empty)
                return;
            System.Drawing.Bitmap image =new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 16.5)), 28);//Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
            Graphics g = Graphics.FromImage(image);//Convert.ToInt32(strValue.Length * 12)
            try
            {
                //生成随机生成器 
                Random random = new Random();
                //清空图片背景色 
                g.Clear(Color.White);
                //画图片的背景噪音线 
                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, y1, x2, y2);
                }

                Font font = new System.Drawing.Font("Arial", 15, (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);