Border (or outline?) of Images stretched in mobile view

Hi, there:

In the home page of my website (URL: primeed.net), I used some thumbnail images and used circular outline and gray border in the image setting. However, the outline (or border?) is stretched to oval shape in mobile view. This is particularly obvious when the mobile phone is flipped to landscape view – it is stretched so much that it is way out of proportion (see attachment).

Is there anyway to fix this? Since I cannot upload more than too images in one reply, I will send you the screenshot for the Image Setting in the next entry.

Thank you very much for your help!

Renee