In 2016 I started working in crypto. I saw a problem with NFTs immediately. They were not really on-chain or immutable. So I embarked on a journey. Now I have created a format that is unique and rock solid. Fits in one page of a smart contract. Here is my journey - 
CryptoCovfefes
https://etherscan.io/token/0x218d9c723464cd066345e004b282476a1995924b#code

No Colored Allowed
https://etherscan.io/address/0x019c748131a079b20d99fd8db94d221de88f5855#code

Jiggleos On-chain
https://etherscan.io/token/0x2e88fb70b11bf2b1cf1a6e2f9853f933c1a4cc2a#code

Stona Lisa
https://etherscan.io/address/0x74db110b0bbb71c1bd450414e594980012ce8748#code

punkPOTUS
https://polygonscan.com/address/0x0892B028c28E0106c6Ee23150a0e8AeB004a82e8#code

I am an expert in on-chain NFT.