How to display portrait and landscape images alternating in the same spot?

Hello,

I've got a community (built on Drupal) and members upload their content including their images.
Some are portrait, some are landscape - could be anything from leaflets to photos.
I have not influence over their images and simply cropping them, is destroying the UX.
The images are currently displayed in a rectangular landscape format.

Is there a HTML / CSS solution to this problem?
Smartphone videos being watched on a desktop have sometimes the same video blurry in the background,...

How to display portrait and landscape images alteating in the same spot?