A copy method used in a copy system or a copy apparatus connected to a cloud server includes steps of: scanning a document to obtain old image data containing an old information block; generating new image data containing a new information block according to the old image data; printing the new image data on a medium; and comparing different generations of original image data, one of which is contained in the old image data, in the cloud server to judge whether improper modifications are present on the original image data or not, and notifying an information office to perform an inspection when the improper modifications are present.