16. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: obtaining an image of a rendered document that includes text; determining a two dimensional geometric shape based at least on a first location in the image of the rendered document of a first space between a first pair of consecutive words, a second location in the image of the rendered document of a second space between a second pair of consecutive words, and a third location in the image of the rendered document of a third space between a third pair of consecutive words, wherein the first space, the second space, and the third space are not all included on a same line of text in the rendered document; generating a document signature based on the two dimensional geometric shape; and generating a query for an electronic counterpart to the rendered document, based at least on the document signature.
16. A non-transitory computer-readable medium storing software comprising instructions executable by one or more computers which, upon such execution, cause the one or more computers to perform operations comprising: obtaining an image of a rendered document that includes text; determining a two dimensional geometric shape based at least on a first location in the image of the rendered document of a first space between a first pair of consecutive words, a second location in the image of the rendered document of a second space between a second pair of consecutive words, and a third location in the image of the rendered document of a third space between a third pair of consecutive words, wherein the first space, the second space, and the third space are not all included on a same line of text in the rendered document; generating a document signature based on the two dimensional geometric shape; and generating a query for an electronic counterpart to the rendered document, based at least on the document signature. 18. The computer-readable medium of claim 16 , the operations comprising: determining a first distance between the first space and the second space determining a second distance between the first space and the third space; and determining a third distance between the second space and the third space, wherein determining the two dimensional geometric shape comprises determining the two dimensional geometric shape using the first distance, the second distance, and the third distance.