Digital image holography (DIH) is an interferometric method that allows one to superpose the states of the device investigated at different times. The interference fringes produced are similar to those obtained by real-time holography and are interpretable in the same way. High-contrast interference fringes are reliably obtained even under nonideal experimental conditions. In DIH a CCD camera captures the superposition of a phase-variant object beam and a temporally constant reference beam. The phase difference between these two beams is calculated. The way this is done differs from digital speckle pattern interferometry and other related methods. The temporal phase shift of the object beam is calculated from the phase difference between object and reference beam at two different times. The resulting interference intensity depends on the phase shift of the object beam.