Cropping of photos in Header Highlight section

Hi, I'm finding that the photos for articles in the Header Highlight section of my home page do not always crop correctly. For example, see the 'road rules' article under the 'Latest Articles' section at the top of theholyfish.com. The image should show the entirety of the road sign, but instead zooms in and crops out the edge. The original photo was much larger, but I have created thumbnails of it in all the theme's standard sizes, including 585 x 439. When viewing the thumbnails in WP Admin, the thumbnails look as I intend. I've tried a couple of different plugins for making thumbnails, but the result is always the same: correct in WP Admin, but not on the site. Some screenshots: This is the image in the media library: https://snag.gy/HaWjJF.jpg The image set as featured in the post (it looks incorrect here, same as when published): https://snag.gy/Uvc9V6.jpg After clicking 'Post Thumbnail Editor' on the post page. The thumbnails in bottom right are those saved for the Helena theme dimensions, and they look correct: https://snag.gy/80P9T3.jpg There is one other thumbnail with the same 585x439 dimensions. It looks different than the ones above, but at least more correct than what appears on the site: https://snag.gy/UMa28P.jpg What do you think is happening? When I 'Inspect Source' in my browser, I see it is fetching this image: https://i0.wp.com/theholyfish.com/wp-content/uploads/2017/06/2013-India-Banno-860-1.jpg?resize=585%2C439 . Perhaps it's taking the original photo and resizing it itself, rather than fetching the thumbnail matching those dimensions that I have manually created? Hope I have explained this problem okay. Thanks, Mat.