A detection system includes: an acquiring unit that acquires document data representative of a document which includes a plurality of pages; a selector that selects, for each page of the document, a first printing sheet which contains a detected element or a second printing sheet which does not contain the detected element such that the first printing sheet is selected for at least one page; a supplier that supplies the first or the second printing sheet selected by the selector; a printer that sequentially prints the document acquired by the acquiring unit on the printing sheets supplied by the supplier; a detector that detects a detected element contained in a printing sheet on which the document is printed by the printer; and a reporter that reports detection of the detected element in a printing sheet by the detector.