The size of your JScrollPane needs to be smaller than the size of your JPanel, try to set the preferred, maximum, sizes of you JScrollPane. You can also compute the size of you JPanel, i.e. the size your images use when displayed, and override the getPreferredSize method of the jpanel to return the actual size of the JPanel.
for more information take a look at this.
How to Use Scroll Panes