What is the "Camera Obscura" effect?
A. Light from a scene passes through the aperture and gets reflected from the mirror placed at the other end of the box.
B. Light from a scene passes from one medium to another and gets refracted.
C. Light from a scene passes through the aperture and passes through a lens placed on the opposite side of the box.
D. Light from a scene passes through the aperture and projects an inverted image on the opposite side of the box.

Hint:A pinhole camera is an optical device which is without a lens but with a tiny aperture, a pinhole in a light-proof box with a small hole in one side. Light from the object passes through the aperture and projects an inverted image on the opposite side of the box, which is known as the camera obscura effect.

Complete step-by-step solution:
The pinhole camera is the simplest form of camera which does not have a lens. A tiny opening on one side of the box is used to focus the light rays coming from an object kept in front of the hole to form an inverted image on the other side of the box. The box of the pinhole camera is effectively made of light proof. The image formed by the pinhole camera is always inverted.
Light from the object passes through the aperture and projects an inverted image on the opposite side of the box. This phenomenon of inversion of the image of an object kept in front of the camera is called the camera obscura effect.
If the size of the hole in a pinhole camera is comparable to the size of the object, then the image becomes thick and the image is a blur. The sharpness of the image formed decreases with increase in size of the hole of the pinhole camera because as the size of the hole of a pinhole camera increases then more light enters and disturbs the formation of the image. To get a sharp and thin image of the object, the hole of the image should be precisely made small.
Therefore, option D is the correct answer.

Note:- The size of the image formed is calculated using the symmetry of the triangle formed from the ray of light coming from the top and bottom of the object to the top and bottom of the image formed.The image formed in a pinhole camera is the real image of the object.