For a nice consistent look and feel for your blog posts, having equally sized (cropped) featured images might be the right choice for you. Your blog has this capability with a thumbnail setting found in the customizer, along with other thumbnail cropping options.
Go to Appearance >> Customize >> Theme Options >> Thumbnail Settings
Depending on the blog layout you choose, you have these options:
For your blog choices, you have the “Large” and “Grid” options. The Grid option will generate thumbnails for the grid, gallery, and list styled layouts.
As a reminder, if you decide to use the Blog Featured Post, make sure you also enable the “Crop image for the Blog Featured Post” option too.
Side Note: Cropping your images when uploading is recommended to use larger sizes. Cropping does not “enlarge” your photos if the original size is smaller than the size to be cropped. However, this theme does force an image to stretch to fill the area it resides in. For best results, we recommend using quality and larger images.