what are the functions of a pinhole camera?

A pinhole camera
is "a simple camera without a lens and with a single small aperture."  Many pinhole
cameras are as a simple as a box with a hole in the side.  Others might be more rudimentary like
a wicker basket or more elaborate like a camera obscura.  A pinhole camera's basic function is
produce an image.  With a pinhole camera, this image is usually upside down and varies in
clarity.  Some people use a pinhole camera to study the movement of the sun over time
(Solargraphy).  A type of pinhole camera is often used to view an eclipse.  Another type of
pinhole camera, the camera obscura, was once used by artists.  The device allowed the artist to
view a scene through a different perspective.  The artist would point the lens of the camera at
the still life scene they wanted to paint.  The camera would frame the image in smaller
perspective thus allowing the artist to see the scene as it might appear painted.  (Of course,
this would eventually lead to photography).  The person using a camera obscura might even trace
the image on a piece of paper and achieve a very accurate copy of the
scene.