Problems with image stretching/size in Sight Theme

Hi,

Would REALLY appreciate if someone could help me figure out what is going on with the featured images on my home page. I have recently changed to Sight theme and have searched to see if anyone else has had this problem but can’t find anything. My featured images are now all stretched and distorted whereas before they automatically cropped and resized themselves perfectly.

Any ideas?

The site is https://www.ohdearism.com

Many thanks!