Bild hinzufügen die Schaltfläche GUI Java

Okay, ich habe versucht, verschiedene Möglichkeiten, aber ich kann nicht auf die Taste zu ändern in ein Bild. Ich weiß, die source file ist richtig, weil wenn ich es hochladen als nur ein image-es funktioniert gut. Hier ist mein code:

ImageIcon start = new ImageIcon("start.png");
    button = new JButton (start);

    add(button);

Mein ganzer code

import java.awt.AWTException;
import java.awt.FlowLayout;
import java.awt.Rectangle;
import java.awt.Robot;
import java.awt.Toolkit;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.InputEvent;
import java.awt.image.BufferedImage;
import java.awt.image.DataBuffer;
import java.awt.image.DataBufferInt;
import java.awt.image.WritableRaster;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;

public class UnfollowGUI extends JFrame{

    private JLabel label;
    private JButton button;

    private ImageIcon bgi;
    private JLabel bgl;

    public static Rectangle gameSquare;

    public static boolean rock = true;
    public static boolean runningMine = true;
    public static int stray = 0;
    public static int strayCount = 0;


    public static void main(String[] args) {
        UnfollowGUI gui = new UnfollowGUI ();
        gui.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); //when click x close program
        //gui.setSize(886, 266);
        gui.pack();
        gui.setVisible(true);
        gui.setTitle("Solid Cloud Inc - Twitter Unfolower");
    }

    public UnfollowGUI(){

        setLayout(new FlowLayout());

        bgi = new ImageIcon(getClass().getResource("tu.png"));
        bgl = new JLabel (bgi);
        add(bgl);

        ImageIcon start = new ImageIcon("start.png");
        button = new JButton (start);

        add(button);

        label = new JLabel ("");
        add(label);

        Events e = new Events();
        button.addActionListener(e);
    }

    public class Events implements ActionListener {


        public void actionPerformed(ActionEvent e) {

            if (e.getSource() == button) {
               label.setText("Searching");
               try {
                Unfollow();
            } catch (InterruptedException e1) {
                //TODO Auto-generated catch block
                e1.printStackTrace();
            }
            }
    }

    }
public static void Unfollow() throws InterruptedException{

        if (rock==true){
            runningMine = true;

        }
        if (strayCount >=2){
            runningMine = false;
            stray = 90000000;
            JOptionPane.showMessageDialog(null, "Program Ended");
            System.out.println("Program ended");
        }


        //System.out.println("look iron start");

        try {
            Robot robot = new Robot();

            while(runningMine == true){
                //while (rock == true)
                //System.out.println("searching");

                gameSquare = new Rectangle(Toolkit.getDefaultToolkit().getScreenSize()); //== game square
                BufferedImage img = robot.createScreenCapture(gameSquare);
                WritableRaster r = img.getRaster();
                DataBuffer db = r.getDataBuffer();
                DataBufferInt dbi = (DataBufferInt)db;
                int[] data = dbi.getData();                 

                for (int x_scale = 0; x_scale < gameSquare.width; x_scale += 1) {
                    for(int y_scale = 0; y_scale < gameSquare.height; y_scale += 1) {
                        int rgb = data[x_scale + gameSquare.width * y_scale];
                        if (stray < 10000000){           //2 sec                                                        

                            if ( rgb == -15817767){ //finds unfollow

                            if (runningMine == true){

                                runningMine = false;
                                stray = 0;
                                int xRock = gameSquare.x + x_scale; //sets the x and y of the point
                                int yRock = gameSquare.y + y_scale;
                                robot.mouseMove(xRock, yRock);

                                robot.mousePress(InputEvent.BUTTON1_MASK);
                                robot.mouseRelease(InputEvent.BUTTON1_MASK);
                                Thread.sleep(800);
                                strayCount = 0;
                                Unfollow();
                                //System.out.println("clicked on Rock");


                            }

                        }
                        else{
                            stray ++;
                            //lookIron();
                        }
                    }
                        else if ((stray>=10000000)&&(stray <20000000)){
                            //skillScreen();
                            //System.out.println("no unfollow buttons");
                            robot.mouseMove(1359, 704);
                            Thread.sleep(500);
                            robot.mousePress(InputEvent.BUTTON1_MASK);
                            robot.mouseRelease(InputEvent.BUTTON1_MASK);
                            Thread.sleep(1000);
                            stray = 0;
                            strayCount ++;
                            Unfollow();


                        }

                    }
                }
            }
        }
        catch(AWTException e) {
            e.printStackTrace();
        }

    }
}