1. Method for optical character recognition (OCR) detection of documents in a self-service machine, in particular an automatic teller machine or cash dispenser, comprising: a) detecting an image of a document by means of a digital video or matrix camera having a detection region; b) establishing an intermediate document image by: i) reducing the detected image, ii) determining a position of a document region, corresponding to the document and also edge pixels in the detected image, iii) detecting straight edge lines of the document region with the aid of the determined edge pixels by using a Hough transformation, iv) determining a rotation angle by which the document region in the detected image must be rotated for alignment at edges of the detection region of the digital video or matrix camera, and v) rotating the document region by the rotation angle, resulting in the intermediate document image; and c) forming a background image by: i) reducing the intermediate document image, ii) after said reducing the intermediate document image, removing smaller details from the reduced intermediate document image by filtering the document region, resulting in the background image; d) creating a brightness map of the background image; and e) binarizing the background image to segment alphanumeric character information.