3. The method of claim 1 further comprising: locating a stored page as a candidate match for the image patch of the target document; and calculating the location within the stored page as a candidate center of the image patch.
3. The method of claim 1 further comprising: locating a stored page as a candidate match for the image patch of the target document; and calculating the location within the stored page as a candidate center of the image patch. 4. The method of claim 3 wherein locating the stored page as the candidate match for the image patch of the target document includes: adding the inverse document frequency for each pair of document features to the accumulator indexed by the document pages on which that pair of document features appears; and in response to the maximum value in that accumulator exceeding the threshold, outputting a corresponding document page as a match to the image patch.