1. An image generation apparatus, comprising: a memory storing avatar data, the avatar data including a plurality of data sets and each of the data sets represents a motion of an avatar in a virtual space; and a processor coupled to the memory and the processor configured to: obtain sensor information that represents a motion of a person in a real space acquired from at least one sensor; determine, for each body region of the person in the real world, a reliability of the sensor information; determine, for each first body region corresponding to the sensor information of which reliability is higher than a threshold, a motion of the first body region based on the sensor information and the avatar data; determine, for each second first body region corresponding to the sensor information of which reliability is lower than the threshold, a motion of the second body region based on the sensor information, the avatar data and a first value that indicates an impression of the person in the real world, the first value being determined based on the motion of the first body region; and generate an avatar image based on the motion of the first body region and the motion of the second body region.