Different Ways to Store Data on top of the Bitcoin Blockchain
Encode data in the number of satoshis being sent to an address.
OP_RETURN is a command in the Bitcoin scripting language that was specifically
added to allow the inclusion of metadata on the blockchain.
Currently 80 bytes of information can be added to a transaction using OP_RETURN in Bitcoin Classic (BTC)
and almost unlimited (~1 GiG) in Bitcoin Satoshi Vision (BSV).
This is an unused 32 bit integer (4 bytes max.) in Bitcoin Classic (BTC) and restore in Bitcoin Satoshi (BSV) for its intended use.
Miners can include up to 100 bytes worth of data in a coinbase transaction (per block).
Encode data in the Address itself. Because the Address encodes data of your choice it cannot have been the result of a derivation from a private key (with extremely high probability) and thus any coins sent to such addresses are lost (or "burnt").
Brute force through keys until you get an address that encodes your data, extremely resource intensive and impractical for anything bigger than a couple of bytes.
These are more complex Bitcoin addresses that require one key out of N to redeem. We can use only one key as a real key (like with a standard address) and encode 32 bytes of data in the remaining N-1 keys.