10. A system for classifying a document image based on its content comprising: a machine-readable storage device having instructions stored thereon; and data processing apparatus operable to execute the instructions to perform operations comprising: accessing a set of features stored in memory; analyzing the document image to determine blocks layout; recognizing the document image to obtain digital content data representing text content or potential graphical content; calculating, based on one or more features from the set of features accessed in the memory, feature values of the document image for the one or more features from the set of features, wherein the feature values are based on the digital content data and the blocks layout; and classifying the document image as belonging to a document class from a set of document classes based on the calculated feature values.
10. A system for classifying a document image based on its content comprising: a machine-readable storage device having instructions stored thereon; and data processing apparatus operable to execute the instructions to perform operations comprising: accessing a set of features stored in memory; analyzing the document image to determine blocks layout; recognizing the document image to obtain digital content data representing text content or potential graphical content; calculating, based on one or more features from the set of features accessed in the memory, feature values of the document image for the one or more features from the set of features, wherein the feature values are based on the digital content data and the blocks layout; and classifying the document image as belonging to a document class from a set of document classes based on the calculated feature values. 13. The system of claim 10 , further comprising performing preliminary processing of the document image to improve visual quality of the document image before the image analyzing and the image recognition steps.