Why does a circular camera lens produce a square image?

Question

Camera lenses a circles but why is the resulting image a square

Answer 1

Because the sensor of a digital camera is rectangular.  

Answer 2

As you suspect it produces a circular image, it's the media (be it film or digital sensor) that is rectangular and the image gets cropped to the shape of the medium.

Answer 3

The imaging chip (ccd, cmos) is always rectangular in shape. The lens is not rectangular for a reason- it will significantly distort the image.

Answer 4

because the media they are putting the image on is rectangle such as film of Sensor. The rest of it is cut off.