Promoted links image links?

I had a promoted links area that has been showing images just fine, but this morning we wanted to change the images.  We uploaded the new images into the Site Assets/Images directory (they are 150x150 pixel png files) and copied the links and updated the items in the promoted links list, but now they are displaying as nothing (white page of paper).  

I searched online and did not find much.  What might I be doing wrong?

Thanks