8. A system for retrieving an electronic document in response to receipt of an image patch, the system comprising: a processor; an indexing module stored on a memory and executable by the processor, the indexing module receiving the image patch, identifying a first two-dimensional structure in the image patch, identifying a second two-dimensional structure in the image patch and identifying a third two-dimensional structure in the image patch; an encoder coupled to the indexing module, the encoder generating a first text string that encodes the first two-dimensional structure into a first one-dimensional structure by specifying a location of the first two-dimensional structure, a first quantized angle measured between a line originating from the first two-dimensional structure and a path joining a center of the first two-dimensional structure to a center of the second two-dimensional structure and a second quantized angle defining a path joining a center of the second two-dimensional structure to a center of the third two-dimensional structure; a retrieval engine coupled to the indexing module, the retrieval engine searching, from a library, for a second one-dimensional structure that is similar to the first one-dimensional structure of the image patch; and a retrieval module coupled to the indexing module, the retrieval module retrieving the electronic document corresponding to the second one-dimensional structure similar to the first one-dimensional structure of the image patch from a document storage.
8. A system for retrieving an electronic document in response to receipt of an image patch, the system comprising: a processor; an indexing module stored on a memory and executable by the processor, the indexing module receiving the image patch, identifying a first two-dimensional structure in the image patch, identifying a second two-dimensional structure in the image patch and identifying a third two-dimensional structure in the image patch; an encoder coupled to the indexing module, the encoder generating a first text string that encodes the first two-dimensional structure into a first one-dimensional structure by specifying a location of the first two-dimensional structure, a first quantized angle measured between a line originating from the first two-dimensional structure and a path joining a center of the first two-dimensional structure to a center of the second two-dimensional structure and a second quantized angle defining a path joining a center of the second two-dimensional structure to a center of the third two-dimensional structure; a retrieval engine coupled to the indexing module, the retrieval engine searching, from a library, for a second one-dimensional structure that is similar to the first one-dimensional structure of the image patch; and a retrieval module coupled to the indexing module, the retrieval module retrieving the electronic document corresponding to the second one-dimensional structure similar to the first one-dimensional structure of the image patch from a document storage. 11. The system of claim 8 , wherein the first, the second and the third two-dimensional structures in the image patch include a Scale Invariant Feature Transform (SIFT) feature in the image patch.