Embodiments are provided to search for a dictionary image corresponding to a target image. The method includes detecting keypoints in a set of dictionary images. The set of dictionary images includes at least one dictionary image having a plurality of pixels. At least one random pair of pixels is selected among the detected keypoints of the dictionary image on the basis of candidate coordinates for pixels distributed around the detected keypoints of the dictionary image. A feature vector of each keypoint of the dictionary image is calculated, including calculating a difference in brightness between the selected pairs of pixels of the dictionary image. The calculated difference in brightness is an element of the feature vector. Keypoints of a target image are detected.