It sounds like you are looking for the scrollBy functionality of jScrollPane 2:
http://jscrollpane.kelvinluck.com/scroll_to.html
Since you only want to scroll horizontally you will use the scrollByX function like so:
$(function()
{
var scrollPane = $('.scroll-pane').jScrollPane();
var api = scrollPane.data('jsp');
$('#your-button-id').bind(
'click',
function()
{
api.scrollByX(200);
}
);
}
Additionally, you mention that your scrollpane contains lots of images. If this is the case you will need to ensure that the scrollpane can correctly calculate it's width by using one of the following two techniques:
http://jscrollpane.kelvinluck.com/image2.html
http://jscrollpane.kelvinluck.com/image.html