1. A method for detecting motion quality error of printed documents in a printing system comprising: printing a document having text lines, each text line comprising a plurality of characters; scanning the printed document to generate a scanned image, the scanned image having the text lines and the characters; determining the orientation of the text lines in the scanned image with respect to a process direction of the printing system; detecting positions in the process direction of the printing system of one of the text lines and the characters in the scanned image; determining position errors in the process direction in the printed document based on the detected process direction positions of one of the text lines and the characters in the scanned image and the determined orientation of the text lines; determining at least one motion quality error of the printing system in the process direction based on the determined process direction position errors; and initiating an activity associated with said printing system in response to a motion quality error having been determined.
2. The method according to claim 1 , wherein determining position errors in the process direction comprises: (i) determining line spacing errors when the text lines are oriented in the cross-process direction, or (ii) determining character spacing errors, character width spacing errors, or both, when the text lines are oriented in the process direction, based on the detected positions of at least one of the text lines and the characters.