1. An apparatus configured to detect a body part from a user image, the apparatus comprising: an image acquirer configured to acquire a first depth image and a second depth image, the second depth image acquired after the first depth image; and at least one processor and a memory, the memory containing computer readable instructions stored thereon, which when executed by the at least one processor, configure the at least one processor to, extract the user image from a foreground of the first depth image, divide the user image into at least one of a single-user image representing non-overlapping users and a multi-user image representing overlapping users, flag the user image extracted from the first depth image, track the flagged user image in the second depth image, determine overlap of the flagged user image in the second depth image, and detect the body part from the extracted user image using a first classifier and a second classifier, wherein the first classifier is configured to classify the body part from the single-user image, and the second classifier is configured to classify the body part from the multi-user image.