1. A method for tracking multiple objects, comprising: (a) obtaining video data including a first image frame and a second image frame, wherein the first image frame is a next image frame of the second image frame; (b) detecting at least one object included in a first subset of the multiple objects from the first image frame; and (b) tracking the multiple objects between the first image frame and the second image frame while step (b) is performed, wherein step (b) includes: selecting at least one key frame corresponding to the at least one object of the first subset from a key frame set for storing an appearance of the multiple objects, extracting a keypoint from the selected at least one key frame, and measuring a pose of the at least one object of the first subset by matching the extracted keypoint with a feature point extracted from the first image frame.