Humans naturally see more width than they do height. Video content is almost wide screen rather than square (Vine is a big exception), but it seems images are most often square now (it didn't always used to be this way). I'm wondering if there's a biological reason for this. For example, maybe square is actually more efficiently and pleasantly processed, so it works for images. However, since there's movement in videos, wider can allow more content which can be useful, but this might also take more effort for people due to scanning their eyes side to side to see what's going on.
I know the growth in square images came along with the growth of mobile (and Instagram), but I don't find that a compelling case to say that square is better for mobile. Instagram could display pics on my fine at 320 x 240 instead of 320 x 320. I suppose that extra height could be precious if making comics, for example, in which you might have a lot of text to fit in a small space, but even then I think people could just learn to be more concise.
So to recap, are there any biologically compelling reason to stick to primarily posting square images (aside from being required to by places like Instagram) or is there a case for posting wide screen images?