Featured images / thumbnails stretched

Dear all,

I am experiencing some trouble with my Featured Images, which are all showing up ‘stretched’ and with a wrong aspect ratio.

When you view the query loop at the bottom of https://hanfugirl.sg/ you will notice that when you resize the browser viewport to a narrower dimension, the blog posts / post titles appear really long, which is bad for readability.

When reading a post, the Featured Images also turn up stretched (horizontally or vertically depending on which direction you resize the browser viewport).

May I know if there is any way to resolve this issue? Grateful for any advice.

Gday,
Nicholas

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