The pictures captured by a camera are made of light or, more specifically, electromagnetic radiation. When you take a photograph, light from the scene enters the camera through the lens and falls onto a photosensitive surface, such as a digital sensor or a film strip.
In the case of a digital camera, the photosensitive surface consists of an array of tiny sensors called pixels. Each pixel detects the intensity of light falling on it and converts it into an electrical signal. This signal is then processed by the camera's electronics and stored as digital data, which represents the picture.
In traditional film cameras, the photosensitive surface is a thin layer of light-sensitive chemicals coated onto a film strip. When light strikes the film, it interacts with the chemicals and creates a latent image. The film is later chemically processed to develop and fix the image, revealing the captured picture.
So, in summary, the pictures inside a camera are representations of the scene captured by the camera's photosensitive surface, which interacts with light or electromagnetic radiation to create the image.