Image without caption not centered

Just converted to this theme, which I think is lovely, but have discovered one problem. When I have images that are (supposed to be) centered, but don’t have a caption, the are displaying aligned to the left margin. This isn’t the best look mixed with captioned images that are centered. As an example, see: https://artofnaturalliving.com/2013/09/12/mini-crab-cake-appetizer/ (last image)