14. A method according to claim 13 wherein the step of generating a first sequence of images from the first document comprises: de-skewing an image of the first document by identifying horizontal lines of text in the image of the first document; and dividing up the image of the first document into lines in the direction of the identified horizontal lines and then dividing up the lines into words in the horizontal direction to obtain the word images.
13. A method according to claim 10 wherein the basic units are words.