I am using Worpress Theme Telegraph with WPZOOM. Occasionally, the images from articles do not appear on the thumbnail in the "Featured Posts" slider on the home page. I have repeatedly tried altering the image (making them wider/narrower, larger/smaller), but for some they just won't show. The website is http://agendabeijing.com. Can you please advise? This is our work website and it's making us look unprofessional.