10. A method of comparing a first document and a second document, wherein the text of each of the first and second documents can be divided up into basic units, the method comprising: generating a first sequence of images of basic units from the first document; generating a second sequence of images of basic units from the second document; comparing the basic unit images of the first sequence with the basic unit images of the second sequence to identify matches between the basic unit images of the first sequence and the basic unit images of the second sequence and hence differences identifying basic units of the first and/or second sequence that do not match and/or for which the difference between matched basic units exceeds a predetermined threshold, wherein the step of comparing includes: identifying matches between the basic unit images of the first sequence and the basic unit images of the second sequence, wherein the step of identifying matches includes minimising a global distance measure being the sum of coarse local distance measures for the basic unit images of the first and second sequences, the coarse local distance measure being a measure of the difference between the basic unit image of the first sequence and the basic unit image of the second sequence; and calculating the fine distance between matched basic unit images of the first sequence and second sequence to identify fine differences between the matched basic unit images identifying basic units for which the difference between the matched basic units exceeds a predetermined threshold; and outputting information about the differences between the first document and the second document.
10. A method of comparing a first document and a second document, wherein the text of each of the first and second documents can be divided up into basic units, the method comprising: generating a first sequence of images of basic units from the first document; generating a second sequence of images of basic units from the second document; comparing the basic unit images of the first sequence with the basic unit images of the second sequence to identify matches between the basic unit images of the first sequence and the basic unit images of the second sequence and hence differences identifying basic units of the first and/or second sequence that do not match and/or for which the difference between matched basic units exceeds a predetermined threshold, wherein the step of comparing includes: identifying matches between the basic unit images of the first sequence and the basic unit images of the second sequence, wherein the step of identifying matches includes minimising a global distance measure being the sum of coarse local distance measures for the basic unit images of the first and second sequences, the coarse local distance measure being a measure of the difference between the basic unit image of the first sequence and the basic unit image of the second sequence; and calculating the fine distance between matched basic unit images of the first sequence and second sequence to identify fine differences between the matched basic unit images identifying basic units for which the difference between the matched basic units exceeds a predetermined threshold; and outputting information about the differences between the first document and the second document. 11. A method according to claim 10 wherein the step of minimising a global distance measure uses a dynamic programming algorithm.