Finding corners in an image - Harris and FAST

A corner can be thought as an intersection of two edges. The mathematical definition of the corners in an image is different, but reflects the same idea; the corner is a point with the following property: moving this point in any direction leads to changes in the small neighborhood of the point. For example, if we take a point on the homogeneous area of an image, moving such a point doesn't change anything in the local window nearby. A point on the edge doesn't belong to a plain region, and once again has directions, movements which don't influence a point's local area: these are movements along the edge. Only corners are movement-sensitive for all directions, and as a consequence, they are good candidates for objects to track or compare. In this recipe, we'll learn how to find corners on an image using two...