1. A computer comprising: a memory; and a central processing unit coupled to the memory and configured to: execute a first estimation process including detecting a marker having a predetermined shape from a captured image obtained from a camera, and estimating first position and posture of the camera at a time when the captured image is captured, based on a shape of the marker, execute a second estimation process including obtaining a map point in a three-dimensional space from the memory, and estimating second position and posture of the camera at the time when the captured image is captured, based on a correspondence between a projection point in which the map point is projected on the captured image and a characteristic point extracted from the captured image, and select the first position and posture or the second position and posture based on a result of comparison between a first translational component of the first position and posture and a second translational component of the second position and posture, wherein the first position and posture are selected when a difference between the first translational component and the second translational component is a predetermined value or greater, and the second position and posture are selected when the difference between the first translational component and the second translational component is less than the predetermined value.