I think the circular sensor case has been brought up before, and I am not entirely sure why we prefer rectangles when nothing in nature is rectangular. Quite a puzzle!
Human technology overwhelmingly prefers flat surfaces and right angles, probably because it is efficient: we can make standard parts flat and rectangular, and build a variety of sizes of objects from these. Just look at a hardware store: the lumber, bricks, piping, flooring, and picture framing and are mainly straight, while plywood and sheetrock are flat. How would you even design a standardized system of components if they were all curved? Wouldn't this severely limit the architecture?
People have made dome homes, but these have turned out to be inefficient oddities: not all of the floor space is usable, and heating and cooling is problematic. Likewise, buildings have been made without rectangular floor plans, but access to rooms and building navigation can become a problem if taken to an absurd degree.
Perhaps there was more flexibility back in the days of craftsmanship, but even the immensely elaborate Gothic structures emphasizes horizontality and verticality, despite the decorative carvings and use of circular arcs. Also note that the non-flat, non-straight, non-ninety degree angle components were placed up high: within sight but not where humans actually had to live.
Flat surfaces and right angles are also intellectually tractable: simple geometries are understandable and easy to deal with, such as calculating the area of floor or wall space when specifying the amount of flooring and paint needed in a room.
On the contrary, nature uses atoms as her standardized building blocks, and these can fit together far more flexibly.
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There have been a number of discussions here about the use of circular sensors, and these would seem to be nothing more than a curiosity, not the least since composing a scene within a circle would be problematic except for the simplest of subjects that can stand a centralized composition. Otherwise, making these sensors would be inefficient: either silicon wafer space would be lost, or an opaque mask would cut off the edges of the sensor, or software in the camera would set the pixels outside of the circle as white.
The JPEG, TIFF, PNG, and as far as I know all other formats only supports rectangles, and creating a new circular image format seems to be unlikely. Also, how would you edit such a round image? Especially if you do perspective distortion correction, which would break the circular format? Would you only allow circular cropping of the image? I can image all sorts of poor rectangular crops that would leave a part of the circle intact, which would be pretty ugly.
