What do you want to know? If someone submits a transaction with a child porn image attached in OP_Return, people running Bitcoin Core 30 will relay that “transaction” around the world.

If a Bitcoin Core 30 Node running a pool has a miner that finds a block, that “transaction” will be posted to the Bitcoin blockchain forever and everyone downloading the full blockchain or running a node from that point forward will be required to download child porn to the computer running their node.