Abstract: An image reading apparatus that includes an image scanning module in which an image sensor device is provided. The image reading apparatus includes an upper housing and a pattern located on the bottom surface of the upper housing and positioned at a position x with reference to the edge of the opening. The upper housing has a bottom surface and is provided with an opening for mounting a transparent platen adapted for supporting a document to be scanned. The opening defines an edge. Responsive to detection of the pattern by the image sensor device, the image reading apparatus determines the distance required to move by the scanning module to reach a predetermined positioning line.