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.Drawing;  
  
public partial class RandomImage : System.Web.UI.Page  
{  
    protected void Page_Load(object sender, EventArgs e)  
    {  
        //输出带有随机验证码的图片  
        CreateCheckCodeImage(this.GenerateCheckCode());  
    }  
  
    /// <summary>  
    /// 随机生成4位随机字符（0-9）(A-Z)  
    /// </summary>  
    /// <returns></returns>  
    private string GenerateCheckCode()  
    {    
        //定义验证码长度  
        int CODELENGTH = 4;  
        int number;  
        string RandomCode = string.Empty;  
        Random r = new Random();  
        for (int i = 0; i < CODELENGTH; i++)  
        {  
            number = r.Next();  
            //字符从0-9,A-Z中随机生成，对应的ASCII码分别为48-57,65-90  
            number %= 36;  
            if (number < 10)  
            {  
                number += 48;  
            }  
            else  
            {  
                number += 55;  
            }  
            RandomCode += ((char)number).ToString();  
        }  
        //在Cookie中保存验证码  
        //Response.Cookies.Add(new HttpCookie("CheckCode",RandomCode));  
        Session["CheckCode"] = RandomCode;  
        return RandomCode;  
    }  
  
    /// <summary>  
    /// 输出包括4位随机数字的图片  
    /// </summary>  
    /// <param name="CheckCode"></param>  
    private void CreateCheckCodeImage(string CheckCode)  
    {    
        //若验证码为空，则直接返回  
        if (CheckCode == null || CheckCode.Trim() == string.Empty)  
        {  
            return;  
        }  
        //根据验证码的长度确定输出图片的宽度  
        int iWidth = (int)Math.Ceiling(CheckCode.Length*15m);  
        int iHeight = 20;  
        //创建图像  
        Bitmap image = new Bitmap(iWidth, iHeight);  
        //从图像获取一个绘图面  
        Graphics g = Graphics.FromImage(image);  
        try  
        {  
            Random r = new Random();  
            //清空图片背景色  
            g.Clear(Color.White);  
            //画图片的背景噪音线10条  
            for (int i = 0; i < 10; i++)  
            {  
                int x1 = r.Next(image.Width);  
                int x2 = r.Next(image.Width);  
                int y1 = r.Next(image.Height);  
                int y2 = r.Next(image.Height);  
                //用银色画出噪音线  
                g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);  
            }  
            //画图片的前景噪音点50个  
            for (int i = 0; i < 50; i++)  
            {  
                int x = r.Next(image.Width);  
                int y = r.Next(image.Height);  
                image.SetPixel(x, y, Color.FromArgb(r.Next()));  
            }  
            //画图片的框线  
            g.DrawRectangle(new Pen(Color.SaddleBrown), 0, 0, image.Width - 1, image.Height - 1);  
            //定义绘制文字的字体  
            Font f = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));  
            //线性渐变画刷  
            System.Drawing.Drawing2D.LinearGradientBrush brush = new    
  
System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue,    
  
Color.Purple, 1.2f, true);  
            g.DrawString(CheckCode, f, brush, 2, 2);  
            //创建内存流用于输出图片  
            using (System.IO.MemoryStream ms = new System.IO.MemoryStream())  
            {  
                //图片格式制定为png  
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Png);  
                //清除缓冲区流中的所有输出  
                Response.ClearContent();  
                //输出流的HTTP MIME类型设置为“image/Png”  
                Response.ContentType = "image/Png";  
                //输出图片的二进制流  
                Response.BinaryWrite(ms.ToArray());  
            }  
        }  
        finally  
        { //释放Bitmap对象和Graphics对象  
            g.Dispose();  
            image.Dispose();  
        }  
    }  
}  
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.Drawing;

public partial class RandomImage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        //输出带有随机验证码的图片
        CreateCheckCodeImage(this.GenerateCheckCode());
    }

    /// <summary>
    /// 随机生成4位随机字符（0-9）(A-Z)
    /// </summary>
    /// <returns></returns>
    private string GenerateCheckCode()
    {
        //定义验证码长度
        int CODELENGTH = 4;
        int number;
        string RandomCode = string.Empty;
        Random r = new Random();
        for (int i = 0; i < CODELENGTH; i++)
        {
            number = r.Next();
            //字符从0-9,A-Z中随机生成，对应的ASCII码分别为48-57,65-90
            number %= 36;
            if (number < 10)
            {
                number += 48;
            }
            else
            {
                number += 55;
            }
            RandomCode += ((char)number).ToString();
        }
        //在Cookie中保存验证码
        //Response.Cookies.Add(new HttpCookie("CheckCode",RandomCode));
        Session["CheckCode"] = RandomCode;
        return RandomCode;
    }

    /// <summary>
    /// 输出包括4位随机数字的图片
    /// </summary>
    /// <param name="CheckCode"></param>
    private void CreateCheckCodeImage(string CheckCode)
    {
        //若验证码为空，则直接返回
        if (CheckCode == null || CheckCode.Trim() == string.Empty)
        {
            return;
        }
        //根据验证码的长度确定输出图片的宽度
        int iWidth = (int)Math.Ceiling(CheckCode.Length*15m);
        int iHeight = 20;
        //创建图像
        Bitmap image = new Bitmap(iWidth, iHeight);
        //从图像获取一个绘图面
        Graphics g = Graphics.FromImage(image);
        try
        {
            Random r = new Random();
            //清空图片背景色
            g.Clear(Color.White);
            //画图片的背景噪音线10条
            for (int i = 0; i < 10; i++)
            {
                int x1 = r.Next(image.Width);
                int x2 = r.Next(image.Width);
                int y1 = r.Next(image.Height);
                int y2 = r.Next(image.Height);
                //用银色画出噪音线
                g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2);
            }
            //画图片的前景噪音点50个
            for (int i = 0; i < 50; i++)
            {
                int x = r.Next(image.Width);
                int y = r.Next(image.Height);
                image.SetPixel(x, y, Color.FromArgb(r.Next()));
            }
            //画图片的框线
            g.DrawRectangle(new Pen(Color.SaddleBrown), 0, 0, image.Width - 1, image.Height - 1);
            //定义绘制文字的字体
            Font f = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic));
            //线性渐变画刷
            System.Drawing.Drawing2D.LinearGradientBrush brush = new

System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue,

Color.Purple, 1.2f, true);
            g.DrawString(CheckCode, f, brush, 2, 2);
            //创建内存流用于输出图片
            using (System.IO.MemoryStream ms = new System.IO.MemoryStream())
            {
                //图片格式制定为png
                image.Save(ms, System.Drawing.Imaging.ImageFormat.Png);
                //清除缓冲区流中的所有输出
                Response.ClearContent();
                //输出流的HTTP MIME类型设置为“image/Png”
                Response.ContentType = "image/Png";
                //输出图片的二进制流
                Response.BinaryWrite(ms.ToArray());
            }
        }
        finally
        { //释放Bitmap对象和Graphics对象
            g.Dispose();
            image.Dispose();
        }
    }
}

<img src="RandomImage.aspx" alt="验证码" id="imgRandom" />

using System.IO;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;

public partial class Default2 : System.Web.UI.Page
{
      private Bitmap validateimage;
      private Graphics g;
      protected void Page_Load(object sender, EventArgs e)
      {
          Response.BufferOutput = true;    //特别注意
          Response.Cache.SetExpires(DateTime.Now.AddMilliseconds(-1));//特别注意
          Response.Cache.SetCacheability(HttpCacheability.NoCache);//特别注意
          Response.AppendHeader("    Pragma", "No-Cache"); //特别注意
          string VNum = MakeValidateCode();
          Session["VNum"] = VNum;//取得验证码，以便后来验证
          ValidateCode(VNum);
      }
      public void ValidateCode(string VNum)
      {
          validateimage = new Bitmap(60, 20, PixelFormat.Format24bppRgb);
          g = Graphics.FromImage(validateimage);
          g.FillRectangle(new LinearGradientBrush(new Point(0, 0), new Point(110, 20), Color.FromArgb(240, 255, 255, 255), Color.FromArgb(240, 255, 255, 255)), 0, 0, 200, 200); //矩形框
          g.DrawString(VNum, new Font("arial", 11), new SolidBrush(Color.Red), new PointF(6, 0));//字体/颜色
          g.Save();
          MemoryStream ms = new MemoryStream();
          validateimage.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
          Response.ClearContent();
          Response.C;
          Response.BinaryWrite(ms.ToArray());
          Response.End();
      }
      string MakeValidateCode()
      {
          char[] s = new char[] { '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z','A','B', 'C','D','E','F','G','H','I','J','K','L','M','N','P','Q','I','S','T','U','V','W','X','Y','Z'};//枚举数组
          string num = "";
          Random r = new Random();
          for (int i = 0; i < 5; i++)
          {
              num += s[r.Next(0, s.Length)].ToString();
          }
          return num;
      }
}

<head id="Head1" runat="server">
    <title></title>
<script language="JavaScript">
    function addFileControl() {
        var str = '<INPUT type="file" NAME="File">'
        document.getElementById('FileCollection').insertAdjacentHTML("beforeEnd", str)
    }
        </script>
    </HEAD>
    <body MS_POSITIONING="GridLayout">
        <form id="upMoreFile" method="post" encType="multipart/form-data" runat="server">
            <asp:label id="Title" Runat="server"></asp:label>
            <P id="FileCollection"><INPUT type="file" name="File">
            </P>
            <P><input onclick="addFileControl()" type="button" value="增加(File)">
                <asp:button id="Upload" Runat="server" Text="上传" Width="56px" OnClick="Upload_Click"></asp:button>
                <input style="WIDTH: 56px; HEIGHT: 24px" onclick="this.form.reset()" type="button" value="重置">
            </P>
            <p>
                <asp:label id="strStatus" runat="server" BorderColor="White" BorderStyle="None" Width="544px"
                    Font-Size="9pt" Font-Bold="True" Font-Names="宋体"></asp:label>&nbsp;</p>
        </form>
    </body>