A method for detecting the width and position of documents in a large-format scanner system by way of recorded image information, wherein the scanner system comprises at least one image capturing element for recording the image information, an optics arranged in front of it and at least one reflector arranged opposite the image capturing elements, characterised by the following steps: S1 pre-processing the image information recorded at the reflector prior to arrival of the document for reducing interferences caused by contamination of the optics and the reflector, S2 rough detection of horizontal and/or vertical transition areas (12, 13) between the reflector and the document comprising the following sub-steps: S2a dividing the scanned image in vertical direction into uniform image strips, S2b ascertaining statistical variables for each image strip, S2c examining the scanned image in the image strips with fixed threshold values for deviations such that if a value of the statistical variables of an image strip exceeds the threshold value, this area is recognised as a vertical transition area between reflector and document, S2d examining the image strips in order to determine the horizontal transition area through forming the mean value row by row and ascertaining sufficiently strong and steep edges, wherein the image strips are rotated from the vertical step by step to an angle of 90°, preferably 45°, and S3 fine recognition of horizontal and/or vertical document edges (10, 11) within the transition areas (12, 13) detected by rough recognition in step S2. S1 pre-processing the image information recorded at the reflector prior to arrival of the document for reducing interferences caused by contamination of the optics and the reflector, S2 rough detection of horizontal and/or vertical transition areas (12, 13) between the reflector and the document comprising the following sub-steps: S2a dividing the scanned image in vertical direction into uniform image strips, S2b ascertaining statistical variables for each image strip, S2c examining the scanned image in the image strips with fixed threshold values for deviations such that if a value of the statistical variables of an image strip exceeds the threshold value, this area is recognised as a vertical transition area between reflector and document, S2d examining the image strips in order to determine the horizontal transition area through forming the mean value row by row and ascertaining sufficiently strong and steep edges, wherein the image strips are rotated from the vertical step by step to an angle of 90°, preferably 45°, and S2a dividing the scanned image in vertical direction into uniform image strips, S2b ascertaining statistical variables for each image strip, S2c examining the scanned image in the image strips with fixed threshold values for deviations such that if a value of the statistical variables of an image strip exceeds the threshold value, this area is recognised as a vertical transition area between reflector and document, S2d examining the image strips in order to determine the horizontal transition area through forming the mean value row by row and ascertaining sufficiently strong and steep edges, wherein the image strips are rotated from the vertical step by step to an angle of 90°, preferably 45°, and S3 fine recognition of horizontal and/or vertical document edges (10, 11) within the transition areas (12, 13) detected by rough recognition in step S2.