A block tool, which can be assembled by a user, is configured with multiple types of blocks and is shot by a camera for capturing a still image or a moving image. The position coordinates of a marker of the square-pillar block in a three-dimensional space are obtained by image recognition. Also, a connecting position and the type of each block, a gradient vector of the square-pillar block, an angle between two blocks constituting the square-pillar block, and the respective blocks' lengths are obtained so as to derive the shape, posture, and position of the block tool, and corresponding information processing is then performed.