A printing device is provided with an imager to capture an output image of the paper after it is printed on. The output image is compared to an input image representing the image being printed to detect any artifacts in the output image and to determine the type of the artifacts. The types of the artifacts include effects caused by dirty drum, low or missing toner, dirty or wrinkled paper, etc. The printing device performs a responsive action based on the type of artifacts detected, including displaying a diagnostic message, stopping the printing, rejecting the sheet, re-printing, printing subsequent pages with a corrective action, etc. Further, another imager is provided to capture an image of the paper before it is printed on, and the image is analyzed to detect artifacts of the input paper, including dirty or wrinkled paper, wrong paper size, paper skew or misalignment, etc.