https://www.cnblogs.com/liushuijinger/archive/2012/09/26/2703558.html
大家对于验证码都很熟悉了，几乎每天都会和它打交道，如注册、登录，论坛回帖等。可以说验证码与我们广大网民的生活工作息息相关。当我们在输入验证码时有人可能会觉得麻烦，虽然验证码让我们有一点小小的麻烦，但是它给我们带来了很大的好处。它可以防止利用恶意程序批量注册、发帖、灌水还能有效的防止黑客暴力破解密码。验证码虽然一般只有简单的几个字符，但是它的作用着实不小啊！下面我们就一起看看如何实现网站中的验证码。
下图为一个含有字母跟数字的简单验证码：
下面我们就来看看它们是如何产生的：
用一般处理程序生成验证码
using System;
using System.Web;
using System.Drawing;
using System.Drawing.Drawing2D;
using System.Web.SessionState;
namespace Web.handler
{
/// <summary>
/// WaterMark 的摘要说明
/// </summary>
public class WaterMark : IHttpHandler, IRequiresSessionState // 要使用session必须实现该接口,记得要导入System.Web.SessionState命名空间
{
public void ProcessRequest(HttpContext context)
{
string checkCode = GenCode(5); // 产生5位随机字符
context.Session["Code"] = checkCode; //将字符串保存到Session中，以便需要时进行验证
System.Drawing.Bitmap image = new System.Drawing.Bitmap(70, 22);
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
int i;
for (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", 12, (System.Drawing.FontStyle.Bold));
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);
g.DrawString(checkCode, font, brush, 2, 2);
//画图片的前景噪音点
g.DrawRectangle(new Pen(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);
context.Response.ClearContent();
context.Response.ContentType = "image/Gif";
context.Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
image.Dispose();
}
}
/// <summary>
/// 产生随机字符串
/// </summary>
/// <param name="num">随机出几个字符</param>
/// <returns>随机出的字符串</returns>
private string GenCode(int num)
{
//验证码中出现的字符
string str = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";//str中的值就是将来会在验证码中出现的字符
char[] chastr = str.ToCharArray();
string code = "";
Random rd = new Random();
int i;
for (i = 0; i < num; i++)
{
//code += source[rd.Next(0, source.Length)];
code += str.Substring(rd.Next(0, str.Length), 1);
}
return code;
}
public bool IsReusable
{
get
{
return false;
}
}
}
}
刷新验证码的HTML及Javascript代码：
<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="Login.aspx.cs" Inherits="nwessystem.Login" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>登录窗体</title>
<link href="../css/login.css" rel="stylesheet" type="text/css" />
<script language="javascript" type="text/javascript">
//刷新验证码的js函数
function changeCode() {
var imgNode = document.getElementById("vimg");
//重新加载验证码，达到刷新的目的
imgNode.src = "../handler/WaterMark.ashx?t=" + (new Date()).valueOf(); // 这里加个时间的参数是为了防止浏览器缓存的问题
}
</script>
</head>
<body>
<p>验证码：<img src="../handler/WaterMark.ashx" id="vimg" alt="点击刷新验证码" onclick="changeCode() " /><asp:TextBox ID="txtCode" runat="server" CssClass="txtcode"></asp:TextBox></p>
</body>
</html>
登录时判断验证码是否正确
using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using BLL;
namespace nwessystem
{
public partial class Login : System.Web.UI.Page
{
protected void btnLogin_Click(object sender, EventArgs e)
{
//检验验证码部分
string code = txtCode.Text.Trim().ToUpper();
string rightCode = Session["Code"].ToString();
//判断验证码是否正确
if (code != rightCode)
{
//验证码输入错误！
Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('验证码错误！');</script>");
return;
}
//检验用户名和密码部分
string name=txtName.Text.Trim();
string pwd=txtPassword.Text.Trim();
bool b = LoginManager.Login(name, pwd);
if (b)
{
//登录成功
Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('登录成功！');</script>");
}
else
{
//登录失败
Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('登录失败，用户名或密码错误！');</script>");
}
}
}
}