An image reader includes a document reading unit, and a control unit that functions as an individual image cutting section, character string detection section, mismatch detection section, judgment section, and correction section. The individual image cutting section cuts out individual images from image data obtained through reading by the document reading unit. The character string detection section detects character strings present on the individual images. The mismatch detection section detects, for the character strings detected by the character string detection section, a mismatching portion by making comparison between the individual images with considering character strings having contents identical or similar to each other as same information. The judgment section judges for the mismatching portions whether a ratio of majority characters reaches a predefined ratio. Upon judging that the ratio of the majority characters has reached the predefined ratio, the correction section replaces a minority character with the majority character.