Thumbnail/Image proportion in search results

I'm updating my basic site that features video and trying to keep the thumbnails in proportion. I'm having mixed results, with some holding their 16x9 aspect ratio and others being a large box, clipping the sides. I don't think I've done anything differently between the two, but I also see they images are listed like this in the code: I'm curious if there is a way to lock proportions that I hit on accidentally with one and not the others. I don't need much more customization, so don't feel the need for the Pro edition.   Would love some help. Here's the key page that shows 2 posts with large boxy images (despite sources being 16x9) and the one that worked correctly. http://www.brokenframepictures.com/category/true-crime/ Thanks!