Since what you post is stored on the blockchain, what you can do is publicly prove that the account you control (with your pass) posted the content at a certain date and no later. So someone who takes the content will always have to answer to the public proof that your account, and only your account, posted it openly on the Steem blockchain before they published it elsewhere.
But you could easily take content from elsewhere and publish it on Steemit before the original author does, so that doesn't really help. There's no way to know the Steem version was the first version.
And that violation would stand there for eternity. (If discovered after the deletion/edit grace period).