Off-topic: How can I include a public message in a transaction??
You can't. The message isn't in the transaction, it's on blockchain.info.
So if I carry out a transaction from my Blockchain.info wallet, can I do that?
Yes, you can do it only on your blockchain.info wallet.
That message is handled only by blockchain.info and the person who receives the payment will not know of the message unless they check blockchain.info
i.e: The public message is a third party addition , handled by blockchain.info and not a real part of the transaction.
