[[File:Aerial True Orthophoto.png|thumb|This photo is assembled from several overlapping photos from UAV, completely removing any residual tilt of the buildings. This is a True Orthophoto.]]
An '''orthophoto,''', '''orthophotograph''' or '''orthoimage''' is an [[Aerial photography|aerial photograph]] or image geometrically corrected ("orthorectified") such that the scale is uniform: the photo has the same lack of distortion as a map. Unlike an uncorrected aerial photograph, an orthophotograph can be used to measure true distances, because it is an accurate representation of the Earth's surface, having been adjusted for [[Topography|topographic relief]],<ref>Smith, Gary S. "DIGITAL ORTHOPHOTOGRAPHY AND GIS." ESRI Conference. http://proceedings.esri.com/library/userconf/proc95/to150/p124.html</ref> [[Barrel distortion|lens distortion]], and [[camera tilt]].
Orthophotographs are commonly used in [[Geographicgeographic Informationinformation Systemssystem]]s ([[GIS]]) as a "map accurate" background image. An orthorectified image differs from "rubber sheeted" rectifications as the latter may accurately locate a number of points on each image but "stretch" the area between so scale may not be uniform across the image. A [[Digital Elevationelevation Modelmodel|digital elevation model (DEM)]] is required to create an accurate orthophoto as distortions in the image due to the varying distance between the camera/sensor and different points on the ground need to be corrected. An orthoimage and a "rubber sheeted" image can both be said to have been "georeferenced" however the overall accuracy of the rectification varies. Software can display the orthophoto and allow an operator to digitize or place linework, text annotations or geographic symbols (such as hospitals, schools, and fire stations). Some software can process the orthophoto and produce the linework automatically.
Production of orthophotos was historically achieved using mechanical devices.<ref>[http://www.bbc.co.uk/archive/aerialjourneys/5320.shtml BBC Tomorrow's World: How maps are corrected and updated using aerial photography and optical machinery. 18 December 1970.]</ref>
