1. An image processing apparatus, comprising: a document input unit that inputs document data of a document; a first identifying unit that identifies a position of a string included in the document; a second identifying unit that identifies a range of a mark given in the document based on an orientation of the string; and a string extracting unit that extracts a string subject to giving the mark, based on the position of the string identified by the first identifying unit and the range of the mark identified by the second identifying unit.