A secure printing technique is described that can identify illegally copied or tampered printed documents. Two kinds of micro vector patterns are faintly printed all over the document as a watermark, where it vanishes upon duplicating the document. The watermark can identify whether it is an original or not and, moreover, check whether it has been tampered with or not because the watermark contains the timestamp and original document information. Our experimental results show that the micro vector patterns are simple and effective detectors and can verify the logitimacy of documents in a short rotation.