Blog feature images getting cropped

Hi, this forum seems to be my place. Thanks for looking into my issue:
Feature images (which are ppt screenshots) of each blog post are being wrongly displayed in two ways.

On the home page, where all the posts are listed, these pictures are cropped on the left and right.
After opening the post, on its individual page, the same pics are cropped on the top and bottom.
How can that be fixed?

(An alternative could be to show “featured image” only on the home page – properly. Then I would need a way to not show that pic inside the blog post)

The page I need help with: [log in to see the link]