1. An object tracking device, comprising: an input terminal configured to receive an input image; and at least one processor connected to the input terminal, wherein the at least one processor is configured to: store a past state of a target object in a past image, the past state including a position, a velocity, a variable which denotes whether the target object was moving or resting when the past image was captured, and a likelihood of a current state of the target object; detect a first object which is an object moving in the input image; detect a second object which is an object resting in the input image; estimate the current state of the target object based on the past state of the target object; and determine whether to prioritize the first object or to prioritize the second object before selecting the first object or the second object as the target object, based on the current state of the target object.