z javadocu pre new BorderLayout:
* Each region may contain no more than one component

do BorderLayout.SOUTH davas dva komponenty, preto to nenfunguje

urob si jeden komponent z toho buttonu a obrazku a ten potom vloz do south,
napr nejak takto:

JPanel southComponent = new JPanel();
southComponent.setLayout(new FlowLayout());
southComponent.add(button);
southComponent.add(image);
        
hlavnipanel.add(southComponent , BorderLayout.SOUTH);