How is a hologram different from an ordinary photograph?

A hologram differs from an ordinary photograph primarily in the amount of optical information it captures and stores.

While an ordinary photograph records only the intensity (amplitude) of light reflected from an object—producing a two-dimensional representation where light and dark areas correspond to the amount of light reflected—holography records both the intensity and the phase of the light waves.123

The phase information represents the degree to which light wave fronts are in step with one another, or coherent. By capturing this phase data, a hologram preserves the exact information regarding the depths and heights of an object's contours. When a hologram is illuminated with coherent light, such as a laser beam, this stored information allows for the reconstruction of a three-dimensional representation of the original object, complete with parallax.213

In contrast, an ordinary photograph is limited to a two-dimensional projection, as the phase information is lost during the standard photographic process.13