1. A computer-implemented method of processing a visual query comprising: on a server system having one or more processors and memory storing one or more programs for execution by the one or more processors: receiving a visual query from a client system; performing optical character recognition (OCR) on the visual query to produce text recognition data representing a textual characters, including a plurality of textual characters in a contiguous region of the visual query; scoring each textual character in the plurality of textual characters; identifying, in accordance with the scoring, one or more high quality textual strings, each comprising a plurality of high quality textual characters from among the plurality of textual characters in the contiguous region of the visual query; identifying, in accordance with the one or more high quality textual strings, a canonical source document matching the visual query; retrieving the canonical source document containing the one or more high quality textual strings; and sending at least a portion of the canonical source document to the client system.