This is a primer on extended Gaussian Images. Extended Gaussian Images are useful for representing the shapes of surfaces. They can be computed easily from: (1) Needle maps obtained using photometric stereo, or (2) Depth maps generated by ranging devices or stereo. Importantly, they can also be determined simply from geometric models of the objects. Extended Gaussian images can be of use in at least two of the tasks facing a machine vision system: (1) Recognition, and (2) Determining the attitude in space of an object. Here, the extended Gaussian image is defined and some of its properties discussed. Here, the extended Gaussian image is defined and some of its properties discussed. An elaboration of non-convex objects is presented and several examples are shown. (Author).