Feature point matching is the operation by which one can put in correspondence points from one image to points from another image (or points from an image set). Image points should match when they correspond to the image of the same scene element (or the object point) in the real world.

A single pixel is certainly not sufficient to make a decision on the similarity of two keypoints. This is why an image patch around each keypoint must be considered during the matching process. If two patches correspond to the same scene element, then one might expect their pixels to exhibit similar values. A direct pixel-by-pixel comparison of pixel patches is the solution presented in this recipe. This is probably the simplest approach to feature point matching, but as we will see, it is not the most reliable one. Nevertheless, in several situations, it can give good results.