your node stores whatever ends up in a block. If you don’t want CSAM on your disk then run a pruned node or don’t run bitcoin at all.

even if its not in a flat contiguous format (op_return) you will still be able to recover images with a line of bash when it gets in your utxo set, like the bitcoin whitepaper.

This you can’t prune and can be done without op_return.

my take: you can’t stop it, adversarial actors will do it to attack bitcoin, stop giving them ideas.

good luck!