[hardwired]

Here you are drawing on the image

Code:

Graphics2D g2 = (Graphics2D)image.getGraphics();
g2.drawString(textString, lastX, lastY);

To draw on the JPanel, use the panels graphic context,
not the graphic context of the image as you did above.

Code:

protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.drawString(textString, lastX, lastY);