How is the image in a mirror created without a lens or pinhole?
From every point in the world there are infinitely many rays going out. How come the image on a mirror is ok, when there is no pinhole to capture exactly one ray from each world point, or a lens to focus all rays coming from one world point onto one image point? I mean, in computer vision we use these models to create images, so the mirror example here confuses me a lot.
There is no real image on the mirror surface. Infinitely many rays arrive to every point of the mirror surface and infinitely many rays reflect from every point of the surface. For example CCD sensor is a polished flat surface that does reflect some amount of light, so if it is exposed (without any optics) it can be considered a kind of a mirror - see here a nice example. You can see your own reflection in such exposed sensor, but at the same time the sensor does not capture your image, because there is no optics to project the real image on the sensor.
The image you see on the surface is created only in your eye thanks to the lens in your eye. It is the very same process that creates the image of the normal (non-reflected) world in your eyes.
Yes, there are infinitely many rays radiating from a single point, but only one of them reaches the eye. Try drawing up a picture of the light rays reflecting off a mirror. For each point that gives off light rays, only one of them reach each eye.
