public class TinyTowerOrganizerInterface extends javax.swing.JFrame {

/** Creates new form TinyTowerOrganizerInterface */
    Image backgroundImage = Toolkit.getDefaultToolkit().getImage("D:/Java/TinyTowerOrganizer/Images/Background.jpg");

public TinyTowerOrganizerInterface() throws IOException {

    initComponents();
    class BackgroundPanel extends javax.swing.JPanel{
        private Image image;
        public BackgroundPanel(Image image){
            this.image = image;
        }
        @Override
        public void paintComponent(Graphics g){
            super.paintComponent(g);
            g.drawImage(image, 0, 0, null);

        }

    }

}

@SuppressWarnings("unchecked")
// <editor-fold defaultstate="collapsed" desc="Generated Code">
private void initComponents() {

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setTitle("Tiny Tower Organizer");
    setFont(new java.awt.Font("Pixelated", 0, 18)); // NOI18N
    setMinimumSize(new java.awt.Dimension(900, 500));
    setName("frame"); // NOI18N
    setResizable(false);
    setUndecorated(true);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 900, Short.MAX_VALUE)
    );
    layout.setVerticalGroup(
        layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
        .addGap(0, 500, Short.MAX_VALUE)
    );

    pack();
}


public static void main(String args[]) {
    java.awt.EventQueue.invokeLater(new Runnable() {

        @Override
        public void run() {
            try {
                new TinyTowerOrganizerInterface().setVisible(true);
            } catch (IOException ex) {
                Logger.getLogger(TinyTowerOrganizerInterface.class.getName()).log(Level.SEVERE, null, ex);
            }
        }
    });
}

import java.awt.*;
import javax.swing.*;
import java.io.*;
import javax.imageio.*;

public class MyApplication extends javax.swing.JFrame
{

/** Creates new form MyApplication */
    Image backgroundImage = Toolkit.getDefaultToolkit().getImage("mong.jpg");

    public MyApplication() throws IOException
    {

        this.setContentPane(new JPanel()
        {

            @Override
            public void paintComponent(Graphics g)
            {
                super.paintComponent(g);
                g.drawImage(backgroundImage, 0, 0, null);
            }
        });

        pack();
        setVisible(true);
    }


    public static void main(String[] args)
        throws Exception
    {
        new MyApplication();
    }
}