1. A method of inputting and preparing data from source documents for storage and subsequent retrieval comprising the steps of scanning each source document and forming signals representative of digitized patterns derived from images of characters and graphics thereon, storing the signals representative of the digitized patterns, selecting segments of the stored signals for further processing, converting signals representative of digitized patterns of characters into a machine code, storing as ambiguous characters the digitized patterns of each character not successfully converted into machine code including storing as ambiguous words each group of characters which includes converted characters and at least one ambiguous character, and storing the digitized patterns of the selected segments correlated with the machine code for subsequent use.