1. A computer-implemented method of identifying documents sharing a common underlying structure, comprising: detecting occurrences of a plurality of predetermined image features in a plurality of document images, wherein at least one of the plurality of predetermined image features is common among instances of a form; indexing the plurality of document images in an image index based on the detected image features; building a graph of connected nodes for the plurality of document images by searching the image index; identifying the documents sharing the common underlying structure using the graph; reproducing the common underlying structure shared by the identified documents; and generating improved images of the identified documents by overlaying the reproduced common underlying structure on document images of the identified documents.