1. A method of generating fine-grain fingerprints for identifying content in a rendered document, the method comprising: applying image-based techniques to identify patterns in a document rendered by an electronic document rendering system, irrespective of a file format in which the rendered document was electronically created, the applying of the image-based techniques including: i. scanning, by at least one electronic processor, the rendered document one scanline at a time to identify image pixels, wherein at each current pixel a determination is made by the at least one electronic processor whether the local neighborhood of pixels corresponding to a local image neighborhood is a member of a new or previously existing local image neighborhood, ii. identifying candidate keypoints at locations in a local image neighborhood of the document, by the at least one electronic processor, and iii. combining the locations of the candidate keypoints to form fine-grain fingerprints indentifying patterns representing content in the document, by the at least one electronic processor.
1. A method of generating fine-grain fingerprints for identifying content in a rendered document, the method comprising: applying image-based techniques to identify patterns in a document rendered by an electronic document rendering system, irrespective of a file format in which the rendered document was electronically created, the applying of the image-based techniques including: i. scanning, by at least one electronic processor, the rendered document one scanline at a time to identify image pixels, wherein at each current pixel a determination is made by the at least one electronic processor whether the local neighborhood of pixels corresponding to a local image neighborhood is a member of a new or previously existing local image neighborhood, ii. identifying candidate keypoints at locations in a local image neighborhood of the document, by the at least one electronic processor, and iii. combining the locations of the candidate keypoints to form fine-grain fingerprints indentifying patterns representing content in the document, by the at least one electronic processor. 9. The method according to claim 1 wherein the candidate keypoint locations tend to congregate one candidate keypoint each in a upper-left and bottom-right corners of each character shape, making the resulting candidate useful for estimating various parameters, including average character width and height, baseline position, and text attributes including ascenders and descenders, skew of the page, and for grouping of characters to form words by measuring the intra-character spacing distance.