1. An optical-symbol-recognition system comprising: one or more processors; one or more memories; one of more data-storage devices; and computer instructions, stored in one or more of the one or more data-storage devices that, when executed by one or more of the one or more processors, control the optical-symbol-recognition system to process a text-containing scanned image of a document by identifying symbol images in the scanned image of the document, for each identified symbol image, starting with a root node of a decision tree stored within the optical-symbol-recognition system and traversing the decision tree until a classifier within a decision-tree node recognizes the symbol image, and representing the symbol image with a symbol code associated with the classifier, and preparing a processed document containing the symbol codes that represent the symbol images in the scanned image of the document and storing the processed document in one or more of the one of more data-storage devices and memories.