Question

Explain why the image was either upright or inverted when you shine a flashlight through a pinhole on a screen.

Answer 1

It happens due to the fact that light travels through air in a perfectly straight line(Fermat's principle) (see diagram below)

The light travels from the top of the object, straight through the pinhole, and straight to the bottom of the screen.

Another light ray travels from the bottom of the tree, straight through the pinhole, and straight to the top of the screen

As a result, the image is inverted.