Most digital orthophoto imagery is captured from aerial photography. Scanned images are rectified to remove distortion so the images are at a consistent map scale. Three types of distortion are removed. Distortion caused by the camera angle and distortion caused by the camera lens.
A digital terrain model is used to remove distortion caused by a landscape's terrain. A typical orthophoto project consists of hundreds of photographs that have been rectified and mosaicked together. Mosaicking involves balancing adjacent photographs' radiometry, which refers to an image's color, brightness and contrast.