public class teste extends JFrame{
ImageIcon imgFundo = new ImageIcon(getClass().getResource("fantasy-2861815_960_720.jpg"));
JLabel lblFundo = new JLabel(imgFundo);

public void janela1() {
    setSize(800,600);
    setVisible(true);
    setLocationRelativeTo(null);
    setResizable(false);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    lblFundo.setSize(10,10);
    add(lblFundo);

}


public static void main(String[] args) {
    teste t = new teste();
    t.janela1();


}