UN - Geographic Information Systems
A representation of a part of the Earth’s surface. However, an image is usually produced using an optical or electronic sensing device. For instance, scanned aerial photographs or remote sensing data are usually referred to as images. In terms of data storage and processing, an image is very similar to a raster or grid.
United Nations, "Handbook on Geospatial Infrastructure in Support of Census Activities", Department of Economic and Social Affairs, Statistics Division, Studies in Methods, Series F No. 103, New York, 2009