Similar to the human eyes and brain, OpenCV can detect the main features of an image and extract these into so-called image descriptors. These features can then be used as a database, enabling image-based searches. Moreover, we can use keypoints to stitch images together and compose a bigger image (think of putting together many pictures to form a 360 degree panorama).

This chapter shows you how to detect features of an image with OpenCV and make use of them to match and search images. Throughout the chapter, we will take sample images and detect their main features, and then try to find a sample image contained in another image using homography.