1. An image processing apparatus, comprising: a storage unit that stores a look-up table having one or at least two pieces of association information for associating the whole or part of one or at least two first images with the whole or part of at least one second image, which is an image whose load on the brain has been adjusted compared with that of the first image and which is an image of the same object as the first image; an image accepting unit that accepts one or at least two images; a mapping unit that acquires the whole or part of one or at least two second images associated with the whole or part of the at least one image accepted by the image accepting unit, using association information from among the one or at least two pieces of association information; and an image output unit that outputs at least one output image, which is the whole of the at least one second image acquired by the mapping unit or a group of part of the at least one second image acquired by the mapping unit.