using System;
using System.IO;
using System.Text;
using System.Web;
using System.Web.UI;
public partial class _Default : Page
{
    protected override void OnInit(EventArgs e)
    {
        string str1 = ResolveUrl("~/image.jpg");
        string str2 = this.Server.MapPath(str1);

        string str = HttpUtility.UrlEncode(Path.GetFileName(str2), Encoding.UTF8).Replace("+", "%20");
        this.Response.ContentType = "image/jpeg";
        this.Response.AddHeader("Content-Disposition", "filename=" + str);
        using (Stream stream = new FileStream(str2, FileMode.Open, FileAccess.Read, FileShare.Read))
        {
            this.Response.Cache.SetExpires(DateTime.Now.AddYears(-1));
            long lengthLeft = stream.Length;
            byte[] buffer = new byte[8192];
            while (lengthLeft > 0L && this.Response.IsClientConnected)
            {
                int count = stream.Read(buffer, 0, 8192);
                this.Response.OutputStream.Write(buffer, 0, count);
                this.Response.Flush();
                lengthLeft -= (long)count;
            }
        }
        base.OnInit(e);
    }
}

<%@ Page Title="Home Page" Language="C#"  AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" %>

<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <system.web>
    <authentication mode="None" />
    <compilation debug="false" />
  </system.web>
</configuration>