A system is disclosed for detecting defects in a printed image to analyze print quality of printers or copiers. The printed image is scanned by the scanner and the printed image data obtained in the scanner is fed back and compared with original image data. The system detects defects in the printed image in a closed loop manner. The printed image data is automatically fed back to a control unit so that a processor compares the printed image data with the original image data to detect defects in the printed image. The system analyzes comparison results to find skew in the printed image.