1. An image processing method for inspecting an image, comprising: creating synthetic image information in which information is synthesized with main image information in a visible state which the human eyes perceive, in an invisible state which is hard to perceive with the human eyes; printing the synthetic image information onto a medium; acquiring an image printed on the medium as an inspection image information; extracting information embedded in the main image information from the inspection image acquired; and determining a fault in the image printed on the medium based on an extraction result of information.