A diagnostic system may comprise an image forming apparatus that forms a diagnostic image on a sheet and an image capturing apparatus that captures an image of the sheet on which the diagnostic image is formed and which has been discharged from the image forming apparatus, and outputs the image captured as a sheet image. The image capturing apparatus may make a diagnosis for a component of the image forming apparatus based on a position of an image deficiency in the sheet image, and output a diagnosis result for the component of the image forming apparatus.