$(document).ready(function(){
  // wrap div around img for shadows
  $("#content_referenties ul img").wrap("<div class='imgwrap'>" + "</div>");
  
  // and vertically center the wrapped images
  $('#content_referenties ul img').each(function(i){
    var ah = $('#content_referenties ul img').eq(i).height();
    var ph = $('#content_referenties ul img').eq(i).parent().height();
    var mh = (ph - ah) / 2;
    $('#content_referenties ul img').eq(i).css('margin-top', mh);
    });
});