随机产生验证码图片---参考代码

前端：

<tr>
<td style="height: 20px" ><div align="center"> 验证码：</div></td>
<td align="left" style=" 277px; height: 20px;" ><asp:TextBox ID="txtCode" runat="server" Height="25px" Width="112px"></asp:TextBox></td>
<td align="center" style="height: 20px" ><asp:Image ID="Image1" runat="server" Width="100px" BorderColor="Gray" BorderWidth="1px" Height="32px" ImageUrl="~/Image.aspx" /></td>
<td align="center" style="height: 20px" ><asp:RequiredFieldValidator ID="RequiredFieldValidator3" runat="server" ControlToValidate="txtCode"
Display="Dynamic" ErrorMessage="请输入验证码" ForeColor="DimGray" Font-Size="10pt">*</asp:RequiredFieldValidator>
&nbsp;</td>
</tr>

Image.aspx

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Image.aspx.cs" Inherits="Image" %>

<!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>无标题页</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
    
    </div>
    </form>
</body>
</html>

Image.aspx.cs

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.IO;
using System.Drawing.Imaging;
using System.Drawing;
public partial class Image : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        string tmp = RndNum(Convert.ToInt16(6));
        Session["verify"] = tmp;
        ValidateCode(tmp);
    }
    private void ValidateCode(string VNum)
    {
        Bitmap Img = null;
        Graphics g = null;
        MemoryStream ms = null;
        int gheight = VNum.Length * 9;
        Img = new Bitmap(gheight, 18);
        g = Graphics.FromImage(Img);
        //背景颜色
        g.Clear(Color.WhiteSmoke);
        //文字字体
        Font f = new Font("Tahoma", 10);
        //文字颜色
        SolidBrush s = new SolidBrush(Color.Red);
        g.DrawString(VNum, f, s, 3, 3);
        ms = new MemoryStream();
        Img.Save(ms, ImageFormat.Jpeg);
        Response.ClearContent();
        Response.ContentType = "image/Jpeg";
        Response.BinaryWrite(ms.ToArray());
        g.Dispose();
        Img.Dispose();
        Response.End();
    }
    private string RndNum(int VcodeNum)
    {
        string MaxNum = "";
        string MinNum = "";
        for (int i = 0; i < 5; i++)//这里的4是验证码的位数
        {
            MaxNum = MaxNum + "5";
        }
        MinNum = MaxNum.Remove(0, 1);
        Random rd = new Random();
        string VNum = Convert.ToString(rd.Next(Convert.ToInt32(MinNum), Convert.ToInt32(MaxNum)));
        return VNum;
    }
}