I assume your button is implemented as a JButton. If so, you may be
able to accomplish your goal by specifically setting its disabled image
icon to the same image as its normal image icon. something like:

 ImageIcon image = new ImageIcon ("some/file.png");
 JButton button = new JButton (image);
 button.setDisabledIcon (image);

You should note that this only impacts the image for the button. the rest
of the button (its border, its text, etc) will be renedered as being disabled.