1. An information processing apparatus, comprising: a first image pickup means to pickup an image of a real space, to thereby obtain a first background image; a first positional relationship estimating unit to estimate, in a case where the first background image includes a first marker image being an image of a marker previously registered and located in the real space, a first positional relationship being a spatial positional relationship of the first image pickup means to the marker based on the first marker image, and to estimate, in a case where the first background image fails to include the first marker image, the first positional relationship based on a displacement of a feature point extracted from the first background image; an image generating unit to generate a first additional image based on the first positional relationship, and to synthesize the first additional image and the first background image, to thereby generate a synthetic image; and a display means to display the synthetic image.