I think this is some (new?) social media trend, my school started doing it too with their images on facebook. Half the image is just a border so the actual image is really low res. I have no idea why they do it though.

Some social media sites and apps like to cut off the sides to fit content onto different screen sizes and aspect ratios.

I think adding a border is an attempt to preserve the essential parts of the images in those situations. It really should not be necessary, but alas modern/stupid problems require modern/stupid solutions.

so it's for drawing attention on social media?