Disclosed is a method for scanning documents by a machine including a scanner that moves back and forth, which is capable of preventing unnecessary consumption of printing ink or toner associated with processing unnecessary data by scanning a block of a document support and storing the scanned data as a reference block, scanning the document and generating a document block, comparing the reference block and the document block and detecting a rightmost location of the document, processing data before the rightmost location as document data and processing data after the rightmost location white or skipping the data after the rightmost location.