An NFT stamp / crypto stamp is a physical stamp that is connected to a digital twin that is stored in the blockchain. This linkage provides complete traceability of all previous owners of the stamp, states its current ownership, makes it easily tradeable and proves its authenticity and uniqueness to ensure that buyers are getting genuine items.

Technically, the Wacken NFT stamps are executed as blockchain tokens in the ERC721 standard, which is widely supported by many blockchain applications.