Instead of sending stenography using bitcoin why not send them using whatsapp since they claim their massages end-to-end encrypted and totally free and i think it's quite secure, bitcoin fees are high especially for small transaction. But if you're looking for more secure i think bitcoin is not the answer it must be monero an untraceable altcoin. Actually technology behind bitcoin the blockchain should be implemented on something that needs a proof without 3rd party or replace archiving method.
i preffer telegram for it,telegram have a bot for developing and free.also we can used/make wallet on telegram
Actually i don't believe with whatsapp claim, because in my country there are some rumor that our intelligent can read whatsapp, i dont know this is true or not but i will never trust third party to involve in my money
whatsapp can hacked and telegram not,
many country denied telegram because pavel durov dont want make back door for telegram,that mean hidden way to listen user