Orthographic views project at a right angle to the data plane. Perspective views project from the surface onto the datum plane from a fixed location.
This photo is properly projected on elevation model, yet on a single building scale, a small tilt is noticeable due. This is an Orthophoto, but not a True Orthophoto (not all vertical features are reprojected).
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 photograph 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 topographic relief,lens distortion, and camera tilt.
Orthophotographs are commonly used in the creation of a Geographic Information System (GIS). 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. 
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Demers, Michael N., (1997). Fundamentals of Geographic Information Systems, John Wiley & Sons.
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