This is pretty straight forward. The only thing I might add is the light doesn't 'spread' so much as the light point will appear 'opposite' positionally within the camera. At least that's my explanation.
Originally known as Camera Obscura. A room, or tent, with a pinhole aperture that projects an image on the backwall or an easel for tracing by an artist or draftsman inside a darkened room. The diameter of the pin hole is related to the focal length, or distance between the pinhole and the capturing surface; the wall, a piece of film, photo paper, whatever. If the diameter of the aperture is too large, like a window, there will not be the inversion and focusing of the image. I think that theoretically, there is an optimum focal length for each pinhloe aperture that will focus perfectly, or am I wrong about that? So, in theory, if the focal length was long enough wouldn't an aperture as large as a window focus an image?
"We often think that when we have completed our study of one we know all about two, because 'two' is 'one and one'. We forget that we have still to make a study of 'and'."
-A. S. Eddington