Private overprint

In philately, private overprints or commercial overprints are overprints applied to postage stamps, postal stationery or revenue stamps by anyone other than the official stamp-issuing entity. These overprints have principally been used as a security measure,^[1] however, propaganda and commemorative examples are also known. When overprinted for security purposes, they serve a similar function to perfins. It is important to distinguish between private overprints and private cancellations.