2. The non-transitory machine-readable storage medium of claim 1 , wherein: the feature is a feature that was previously determined to be a feature capable of distinguishing the document image or a document that comprises the document image, and the feature was previously identified by analysis of a plurality of training documents each having at least one unique feature different from at least one of the other training documents.
7. The non-transitory machine-readable storage medium of claim 2 , wherein: the associating the document image with the class further comprises: determining a value from the document image, and determining a reliability index of the decision tree, wherein the reliability index is based on the identified feature of the document image.