An optical image retrieval method, which makes optical input devices work on transparent media, which method generates a light and projects it in a vertical direction. The light is directed to a light-splitter and transmitted to an image contacting surface under a transparent medium. Optical image signals retrieved on the image contacting surface are reflected to the light-splitter, and then an optical axis of the image signals is reflected to a lens by the light-splitter once or more. Finally, the lens will focus the image signals onto an image detecting element.