Thanks! I just discovered that the problem only occurs using the Microsoft Edge browser, everything is fine on Chrome and Firefox.
I've updated the initial post to indicate that.
Yup, in Safari both images seem identical ,with smooth rounded corners on my Mac
You are absolutely correct to note that it is an Edge Browser bug. Safari, Chrome and Firefox should display images properly. I’ll ask Kevin if there is an easy fix for it.
Thanks Vilen! If it's easily fixable that would be great since it's pretty ugly. But given that it's just one browser it's not as bad as I initially thought.
In case it's useful, I am going to upload 2 screenshots to show how the photos look in Cake on Microsoft Edge. Sorry, I should have done this before!
This is the linked photo:
This is an uploaded photo: