验证码

一、造一个验证码的图片

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Drawing;
public partial class YZM : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //造一个图片
        Bitmap img = new Bitmap(60, 30);
        //生成个随机数
        string str = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890";
        Random rand = new Random();
        string code = "";
        for (int i = 0; i < 4; i++)
        {
            int start = rand.Next(str.Length);
            code += str.Substring(start, 1);
        }
        Session["yzm"] = code;
        //把随机数画到图片上
        SolidBrush brush = new SolidBrush(Color.White);
        Font font = new Font("Lucida Sans Unicode", 14);
        Graphics g = Graphics.FromImage(img);

        //a.把图片背景涂白
        g.FillRectangle(brush, 0, 0, 60, 30);
        //b.给画笔换个颜色
        brush.Color = Color.Red;


        g.DrawString(code, font, brush, 0, 0);

        //把图片保存到输出流中去
        img.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);

        Response.End();
    }
}

二、建立一个验证的界面并实现

　　　 需要控件textbox，image，button

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

public partial class Default5 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }
    protected void Button1_Click(object sender, EventArgs e)
    {
        if (Session["yzm"].ToString() == TextBox1.Text)
        {

        }
    }
}

<script language="javascript">
        function changePIC() {
            var img = document.getElementById("Image1");
            img.setAttribute("src","yzm.aspx?id="+Math.random());
        }
    </script>