Photo sensor

The digital cameras that we use have light sensors instead of film. They are 
grids of photo-electric cells, which means that when light hits them, they develop an positive electrical charge. This happens because the energy in light causes electrons to be scattered. Electrons are the negatively-charged parts of an atom that circulate around the atom's centre, or nucleus. If there are less of them, then the remaining charge is positive. The camera's microprocessor converts the electrical charges into numbers - 1s or 0s, and these numbers are in turn allocated a visible tone in shades of grey. This produces the photograph that we see.
Kevin Smith, of MetPrep Ltd photographed the CCD - the charge-coupled device in the sensor and magnified it 1000 times to show what it looked like.