An image processing apparatus, comprising: an interface through which scanned image data obtained by scanning a designated region, is acquired; and a processor configured to extract a contour line (100, 200, 300) representing a document area from the scanned image data, extract vertices of the contour line by calculating a curvature at each point of the contour line, determine whether a plurality of the original documents is present in the document area based on the vertices, extract document image data of each original document from the scanned image data, and generate a plurality of files, each of the files including document image data for one of the original documents; characterised in that: the processor is configured to extract first to third vertices of the contour line that are adjacent to one another and form a right angle or an approximate right angle, estimate a fourth vertex from the first to third vertices such that the first to fourth vertices form a rectangle or an approximate rectangle, and extract document image data of an original document from the scanned image data based on the rectangle or the approximate rectangle; and the processor is configured to determine whether or not the rectangle is formed within the document area and extract the document image data of the original document from the scanned image data if the rectangle is formed within the document area. an interface through which scanned image data obtained by scanning a designated region, is acquired; and a processor configured to extract a contour line (100, 200, 300) representing a document area from the scanned image data, extract vertices of the contour line by calculating a curvature at each point of the contour line, determine whether a plurality of the original documents is present in the document area based on the vertices, extract document image data of each original document from the scanned image data, and generate a plurality of files, each of the files including document image data for one of the original documents; characterised in that: the processor is configured to extract first to third vertices of the contour line that are adjacent to one another and form a right angle or an approximate right angle, estimate a fourth vertex from the first to third vertices such that the first to fourth vertices form a rectangle or an approximate rectangle, and extract document image data of an original document from the scanned image data based on the rectangle or the approximate rectangle; and the processor is configured to determine whether or not the rectangle is formed within the document area and extract the document image data of the original document from the scanned image data if the rectangle is formed within the document area. the processor is configured to extract first to third vertices of the contour line that are adjacent to one another and form a right angle or an approximate right angle, estimate a fourth vertex from the first to third vertices such that the first to fourth vertices form a rectangle or an approximate rectangle, and extract document image data of an original document from the scanned image data based on the rectangle or the approximate rectangle; and the processor is configured to determine whether or not the rectangle is formed within the document area and extract the document image data of the original document from the scanned image data if the rectangle is formed within the document area.