1. An information processing apparatus comprising: an acquiring unit that acquires numeral string data, the numeral string data extracted from image data by an extracting unit, including a plurality of numeric elements; a creating unit that encodes each numeric element in the numeral string data to create code string data by assigning a code to each numeric element in the numeral string data based on (i) a magnitude relation, which is determined by comparing a numeric element to be coded and at least one adjacent numeric element (ii) and conversion information, the conversion information associating magnitude relations with assignable codes; a storage unit stores therein the code string data as registration information and the image data in an associated manner; and a searching unit that searches for the image data having the registration information that matches search information, the search information being the code string data encoded by the creating unit.