The invention relates to an image scanning system which is connected to a computer host and comprises a display panel, an analog-to-digital conversion unit, a memory and a control circuit, wherein the display panel comprises an optical detection array, the optical detection array is used for sequentially scanning object images placed on the display panel according to a plurality of gate drive signals of the display panel and producing a plurality of corresponding analog optical detection signal; the analog-to-digital conversion unit is used for converting the received analog optical detectionsignals to digital optical detection signals; and the control circuit is used for sequentially comparing gray scale values in the digital optical detection signals by utilizing a threshold value, defining that all the gray scale values belong to valid data or invalid data and storing the gray scale values to corresponding addresses of the memory, and the control circuit is further used for transferring the address information which corresponds to the valid data recoded in the memory and leading the computer host to reconstruct the object images.