The class of cameras that are based on ionization sensors, which includes the most common charge-coupled device (CCD) and vidicon cameras, is examined. Camera signals are shown to be corrupted by direction-dependent stationary electronic noise sources and fluctuations due to the statistical nature of the sensing process. The authors develop and test a model of the inherent noises in cameras. These results are confirmed by measurement, and they suggest a locally stationary model of noise for adaptive signal processing.