An image processing system comprising: an image reading apparatus that reads an original and outputs image data of the original; and an image processing apparatus (30, 730, 1030) that is connected to the image reading apparatus, and processes image data input from the image reading apparatus, wherein the image reading apparatus includes a scanner unit that scans the original and generates the image data, a first transmitting unit that transmits the image data generated by the scanner unit, wherein the image data is transmitted by the first transmitting unit while the scanner unit scans the original, a detecting unit that detects a predetermined particular image from the image data, and a second transmitting unit that transmits a detection result of detecting the particular image, and the image processing apparatus (30, 730, 1030) includes a receiving unit that receives the image data and the detection result from the image reading apparatus, a storing unit that stores the image data received by the receiving unit in a first storage unit, a determining unit that determines whether the detection result is received, and a restricting unit (31d, 1031d) that restricts, when the determining unit determines that the detection result is received, usage of the image data stored in the first storage unit, characterized in that the image reading apparatus further includes a replacing unit that replaces, when the detecting unit detects the particular image, image data that is generated after detecting the particular image with a predetermined mask image, and when the detecting unit detects the particular image, the first transmitting unit sequentially transmits the mask image to the image processing apparatus (30, 730, 1030). an image reading apparatus that reads an original and outputs image data of the original; and an image processing apparatus (30, 730, 1030) that is connected to the image reading apparatus, and processes image data input from the image reading apparatus, wherein the image reading apparatus includes a scanner unit that scans the original and generates the image data, a first transmitting unit that transmits the image data generated by the scanner unit, wherein the image data is transmitted by the first transmitting unit while the scanner unit scans the original, a detecting unit that detects a predetermined particular image from the image data, and a second transmitting unit that transmits a detection result of detecting the particular image, and the image processing apparatus (30, 730, 1030) includes a receiving unit that receives the image data and the detection result from the image reading apparatus, a storing unit that stores the image data received by the receiving unit in a first storage unit, a determining unit that determines whether the detection result is received, and a restricting unit (31d, 1031d) that restricts, when the determining unit determines that the detection result is received, usage of the image data stored in the first storage unit, characterized in that the image reading apparatus further includes a replacing unit that replaces, when the detecting unit detects the particular image, image data that is generated after detecting the particular image with a predetermined mask image, and when the detecting unit detects the particular image, the first transmitting unit sequentially transmits the mask image to the image processing apparatus (30, 730, 1030).