Ordinals: Accidental Revival of Bitcoin NFTs

Bitcoin was designed to be a peer-to-peer payment system, but that doesn’t stop people from attempting to utilize the Bitcoin network for other usages, such as on-chain NFTs. 

Counterparty was one of the earliest Bitcoin-based NFT projects that facilitated the creation of collections such as Rare Pepes in 2016, which predated most Ethereum-based NFTs. It used the OP_RETURN function that enabled users to embed up to 80 bytes of arbitrary data in a single transaction.