This seems specific to MobileFrontend Beta mode. It does not happen in the default/stable mode.
Whenever the page's default associated image is of portrait aspect ratio, the banner brings negative value to the reading experience.
For example: <https://en.m.wikipedia.org/wiki/Tank_Girl_(film)>
Short the top portion of someone's hair. Poorly cropped and rather pixelated due to it being stretched beyond the nominal size of the original photo. Presumably in a situation like this (bad aspect ratio, image too small) it may be better left out.
Origin of the image:
 If the autogenerated image by page images is not landscape it should not be used