1. An object detection apparatus mounted in a system, the apparatus comprising: a storage storing plural image recognition dictionaries each describing reference data for an object to be detected and plural image recognition techniques each used to detect the object from an input image captured by an imaging unit with use of one of the plural image recognition dictionaries; an acquirer configured to acquire either or both of information indicative of an external environment around the system and information indicative of an operating state of the system; a determiner configured to determine an environmental condition with respect to the input image according to the information acquired from the acquirer; a setter configured to set, for each of plural image recognition methods predefined for respectively different assumed environmental conditions, a weighting factor according to the environmental condition determined by the determiner, each image recognition method being a combination of one of the plural image recognition dictionaries and one of the plural image recognition techniques; and a detector configured to detect the object in the input image by applying each of the plural image recognition methods to the input image to obtain image recognition results reflecting the weighting factors set by the setter for the respective image recognition methods, and then collectively evaluating the image recognition results.