Mam ten kod do centrowania pionowo obrazów w pęczku div.

function centerImages(parent, image) {
    var parent_height = $(image).parent().height();  
    var image_height = $(image).height();  
    var top_margin = (parent_height - image_height)/2;  
    $(image).css( 'margin-top' , top_margin);
}
centerImages(".clients li", ".clients li img");

.. ale to nie działa.