asp.net生成验证码,通过session验证

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Drawing;
using System.Web.SessionState;

namespace WebApplication3
{
/// <summary>
/// Handler1 的摘要说明
/// </summary>
public class Handler1 : IHttpHandler,IRequiresSessionState
{

public void ProcessRequest(HttpContext context)
{
string g = GenerateCheckCode();
context.Session["checkcode"] = g;
CreateCheckCodeImage(g);

}

public bool IsReusable
{
get
{
return false;
}
}

private string GenerateCheckCode()
{
int number;
char code;
string checkCode = String.Empty;

System.Random random = new Random();

for (int i = 0; i < 5; i++)
{
number = random.Next();

if (number % 2 == 0)
//生成'0'-'9'字符
code = (char)('0' + (char)(number % 10));
else
//生成'A'-'Z'字符
code = (char)('A' + (char)(number % 26));

checkCode += code.ToString();
}

//HttpContext.Current.Response.Cookies.Add(new HttpCookie("checkcode", checkCode));

return checkCode;
//两个字符相加等于=asicc码加
}

private void CreateCheckCodeImage(string checkCode)
{
if (checkCode == null || checkCode.Trim() == String.Empty)
return;
//(int)Math.Ceiling((checkCode.Length * 12.5)),22
System.Drawing.Bitmap image = new System.Drawing.Bitmap(80, 30);
Graphics g = Graphics.FromImage(image);

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 < 5; i++)
{
int x1 = random.Next(image.Width + 10);
int x2 = random.Next(image.Width + 10);
int y1 = random.Next(image.Height + 10);
int y2 = random.Next(image.Height + 10);

Pen p = new Pen(Color.Gray, 4);
g.DrawLine(p, 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, System.Drawing.Color.DarkRed, 1.2f, true);
g.DrawString(checkCode, font, brush, 5, 5);

//画图片的前景噪音点
for (int i = 0; i < 200; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height);

image.SetPixel(x, y, System.Drawing.Color.FromArgb(random.Next()));
}

//画图片的边框线
g.DrawRectangle(new System.Drawing.Pen(System.Drawing.Color.Silver), 0, 0, image.Width - 1, image.Height - 1);

System.IO.MemoryStream ms = new System.IO.MemoryStream();
image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);

HttpContext.Current.Response.ClearContent();
HttpContext.Current.Response.ContentType = "image/jpg";
HttpContext.Current.Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
image.Dispose();
}
}
}
}

然后在界面中调用

<img alt="验证码" src="Handler1.ashx" onclick="this.src='Handler1.ashx?abc='+Math.random()"/>

然后在验证程序中验证

if (String.Compare(Session["checkcode"].ToString(), TextBox4.Text, true) == 0)
{
Label1.Text = "通过";
}
else
{
Label1.Text = "失败";
}