Progress Bar with static Image

using System;
using System.Windows.Forms;
using System.Drawing;
using System.Threading;

class Program
{
class ImageForm : Form
{
static void Main()
{
Application.EnableVisualStyles();
Application.Run(new ImageForm());
}
private ProgressBar pb;
public ImageForm()
{
Button button = new Button();
button.Text = "Load";
Controls.Add(button);
button.Click += new EventHandler(button_Click);
pb = new ProgressBar();
pb.Dock = DockStyle.Bottom;
pb.Style = ProgressBarStyle.Marquee;
pb.Visible = false;
Controls.Add(pb);
}

void button_Click(object sender, EventArgs e)
{
pb.Visible = true;
ThreadPool.QueueUserWorkItem(LoadImage);
}
private void LoadImage(object state)
{
Thread.Sleep(5000); // to make it look slower to demo
Image img = Image.FromFile(@"C:\WINDOWS\Coffee Bean.bmp");
Invoke((MethodInvoker) delegate {
BackgroundImage = img;
pb.Visible = false;
});
}
}
}