Most photographs are oblong. Fewer are square.
Why don’t we see images that are hexagonal, or octagonal – sometimes we see circular ones, but then only because they’ve been taken with a fisheye lens on a full frame camera. Why not oval…
The reality is that you can make photographs any shape you want, but the vast majority are oblong.
Partly I can see the logic. Photographic paper is now, and always has been a particular shape, and it’s much easier to obtain mounts with specific sized holes cut in them. In fact if you go to most framing sites online, they offer ‘standard’ size mounts with ‘standard’ cut outs….
Think of it this way, a lens makes a round image, but you only see the rectangle because of the nature of the camera.
Tradition makes oblongs – artists can make them any shape they choose….. so why don’t we?