Automatic detection method for paper feeding size

The invention discloses an automatic paper feeding size detection method. The paperweight is marked with a plurality of mark points arranged in the paperweight direction different from the paper feeding direction. The paper weight direction is different from a paper feeding direction, and the automatic paper feeding size detection method comprises the following steps of: controlling an image sensor to continuously sense a plurality of mark points of the paper weight to obtain a scanning image comprising a plurality of continuous column images when a piece of paper passes between the paper weight and the image sensor; determining a first side length of the paper based on a covering range of the plurality of mark points covered by the paper in the plurality of column images; and determining a paper size of the paper according to the first side length. A plurality of continuous column images which can be combined into scanning images are sensed when paper passes between a paperweight and an image sensor, the sid