Abstract: An automated method of matching an input document to a set of documents from a document repository. A signature database is stored, the signature database including a document identifier and signatures generated by a first signature generator for each of the set of documents. The input document is received and signatures are generated for the input document using a second signature generator, and the signature database is searched using the signatures generated for the input document. The first and second signature generators are configured such that different numbers of signatures are generated for a same document. Other embodiments, aspects and features are also disclosed.