1. A method of estimating an attitude of a camera, wherein the camera acquires an intensity image and a depth image, the method comprising steps of: collecting information about images captured by the camera in an environment in which a planar marker is disposed; determining a position of the planar marker from images in which the planar marker is captured without occlusion; extracting localized feature points for calculating the attitude of the camera for each frame from the intensity image and the depth image of each frame acquired by imaging; performing association between the extracted feature points, one-to-one between frames, based on a distance between descriptors; estimating an approximate attitude of the camera during imaging of a specified frame in which a marker hidden by an occlusion is captured, based on the association between the feature points; predicting an approximate position of the marker in relation to the specified frame based on the position of the marker and the approximate camera attitude; extracting point groups within a predetermined distance from the predicted approximate position of the marker, through converting a three-dimensional point included in the depth image of the specified frame to a world coordinate system using the approximate attitude of the camera; and re-estimating the attitude of the camera during imaging of the specified frame by determining a camera attitude that optimizes an evaluation function conditioning a distance between a marker neighboring point included in the point groups and an estimation plane on which the marker is positioned.