1. An optical information detecting method comprising: detecting an image of a source data page containing a frame mask by the use of an optical detection region within respective 1:N (where N is greater than 1) excessive detection pixels; monitoring a light intensity of the detected image and determining a matching state of the frame mask; determining an arrangement pattern of valid detection pixels of the detection pixels in accordance with the determined matching state of the frame mask and detecting sampling detection pixels; and sampling an image of the sampling detection pixels from the detected image and reproducing the image of the source data page.