1. A watermarked image generation apparatus for embedding target data in an original image to generate a watermarked image, the watermarked image generation apparatus comprising: an acquiring unit that acquires a captured image provided by capturing a part of the watermarked image, a target-data embedding unit that embeds the target data in respective plural embedding areas contained in the original image so as to arrange a same target data in lines repeatedly, to generate the watermarked image; a marker-image embedding unit that embeds in the watermarked image a plurality of marked images used for identifying the plural embedding areas; and a density adjustment unit that changes a density of a non-embedding area, which is an area in the watermarked image other than the plural embedding areas, wherein the plural embedding areas are separated from each other so that no portion of each embedding area shares a common portion with another embedding area, and a detecting unit that detects the marked images contained in the captured image; an identifying unit that identifies a plurality of partial embedded areas contained in the captured image based on positions of the marked images detected by the detecting unit, each of the partial embedding areas being a portion of the embedding area; an extraction unit that analyzes some of the plurality of partial embedding areas, and that extracts plural pieces of partial target data, each of pieces of partial target data being a portion of the target data; and a target data re-generating unit that (i) determines in which portion each of partial target data covers in the target data based on relative positions between the marked images and partial embedding areas corresponding to the partial target data, (ii) combines the extracted pieces of partial target data according to a result of the determination, and (iii) re-generates the target data.