If you have a high quality official promotional non-poster image, however, it's vertical, is it appropriate to still use it as a backdrop? (Provided cropping it like so doesn't "destroy" the image).
Yes, it's fine as long as the resulting backdrop look good. :smiley_cat:
What does that mean for using them as no language posters? :spy:
Most no language posters are a textless version of an official poster:
I wouldn't recommend adding any random vertical promo images as no language posters. But keep in mind that non-poster images can be used to create custom poster when necessary, as long as the images make okay posters.