I was in an office and noticed two perfect circles of light on the carpet. Here’s one captured on my hand:
I followed the light up toward the source and figured out that it was sunlight, of course, passing through one of the oval openings in the blinds, where the strings pass through. I’m pretty sure you aren’t seeing the sun outlining the edges of the hole with its light, though. The hole isn’t circular. This is an image of the sun projected inside the room.
I normally think of pinhole cameras only in the context of eclipses. Poke a tiny hole in the end of a shoebox and you can watch the moon cross the surface of the sun. Well, apparently you can get a pinhole camera in your office, too. I suppose this is actually a camera obscura, since I’m not taking a picture with it–a dark room with an image from the outside projected in reverse on the wall.
If you ever happen to be in a place with a solar eclipse, or even a partial solar eclipse, look under a tree. The tiny gaps between the leaves project countless images of the sun.
The Kodak website has instructions on how to make your own pinhole camera–they even tell you how long your exposure should be, depending on which film you’re using.