Hi,
I just noticed today while browsing emby (the webapp), The aspect ratios aren't maintained for some cast images.
For example,
In the movie American Made, there is a member of the cast Jesse Plemons, his pic seems to be squeezed horizontally, making it look a bit weird.
The exact pic in question can be found here for your testing,
https://image.tmdb.org/t/p/original/4fdE4D8e2DEtFL4QgdorQOAI9RT.jpg
I have narrowed down the issue to,
https://github.com/MediaBrowser/emby-webcomponents/blob/master/cardbuilder/card.css#L277
Changing background-size to 'cover' seems to have solved the problem, and from my testing there doesn't seem to be any negative effect to the other images.
I hope that helps you figure it out.
Thanks,