1. An information extraction apparatus comprising: an obtaining unit that obtains image data pertaining to a printed material, in which information is embedded by additionally printing multiple types of patterns in a matrix; a line-segment-sequence calculating unit that calculates a plurality of substantially-vertical-line-segment sequences, each of which is obtained by connecting patterns arranged in a substantially vertical row in the image data with a polygonal line, and calculates a plurality of substantially-horizontal-line-segment sequences, each of which is obtained by connecting patterns arranged in a substantially horizontal row in the image data with a polygonal line; a search unit that searches, for each combination of one substantially-vertical-line-segment sequence of the substantially-vertical-line-segment sequences and one substantially-horizontal-line-segment sequence of the substantially-horizontal-line-segment sequences, substantially-vertical line segments that form the one substantially-vertical-line-segment sequence and substantially-horizontal line segments that form the one substantially-horizontal-line-segment sequence for a substantially-vertical line segment and a substantially-horizontal line segment that intersect with each other; an intersection-point calculating unit that calculates a point of intersection between the substantially-vertical line segment and the substantially-horizontal line segment having been found by the search unit as a position of a pattern; and an extracting unit that extracts the information embedded in the printed material by identifying types of patterns at positions calculated by the intersection-point calculating unit.