Anyone Know How NOT to Stretch Thumbnails?

I’m using YARPP in the sidebar and we mainly have movie posters for featured images. The issue is, YARPP stretches those and makes them look poor.

Is there a way to keep this from happening that will still allow for non-movie posts with normal images to display properly too?

Thanks and Happy Holidays to all!

https://www.ads-software.com/plugins/yet-another-related-posts-plugin/