An X-ray machine is a specialized camera

The x-ray technician position had a steep learning curve. Taking x-rays is a lot like snapping black and white pictures, but the radiation beam is more intense. A black and white camera gathers light waves coming from an object and places the incoming light stream onto film in the back of a camera. An x-ray machine generates photons with a higher energy and shorter wavelength than regular light waves.

This shorter wavelength allows the photons to travel through soft tissue. Unlike a regular camera where light bounces off a person and enters the film at the back of a camera, the lower wavelength photons of an x-ray can be used to see through the soft tissue. If a person places his hand between the x-ray head and the film and a radiograph is taken the photons will travel through the soft tissue of the hand and expose that part of the X-ray film. Conversely, bones of the hand are too dense to allow these photons through, and the underlying region on the X-ray film will remain unexposed.

The developed film appears in the usual black, and white; the unexposed areas of bone come out white while the soft tissue areas the photons traveled through coming out dark.