As long as the hole is small enough, its shape, whether square, round or oblate, has no influence on the clarity and shape of the image.
Aperture imaging, about 24,500 years ago, China scholar-Mo Zhai (Mozi) and his students made the world's first pinhole inverted image experiment, explained the reasons of pinhole inverted image, and pointed out the essence of light straight line. This is the first scientific explanation for the straight-line propagation of light.
Blocking a plate with a small hole between a wall and an object will form the reflection of the object on the wall. We call this phenomenon pinhole imaging. Moving the middle board back and forth will change the size of the image on the wall, which shows the nature of light propagating along a straight line.
Extended data:
Other applications of pinhole imaging principle;
Light travels in a straight line in the same uniform medium. Examples of its application in production and life include: arranging in a straight line, "three points and one line" in shooting, laser collimation, carpenter checking whether the edge of the board is straight, shadow play and so on.
Eclipse: When the moon turns between the sun and the earth and they are in a straight line, the moon blocks the light that the sun shines on the earth, and the earth is in the shadow of the moon, forming an eclipse;
Eclipse: When the earth is located between the moon and the sun, the sun cannot shine on the moon. When observing the moon on the earth, there is a shadow in one area. This is a solar eclipse, which is formed by the linear propagation of light.
Baidu encyclopedia-pinhole imaging