
Technically all original works that exist in tangible form are covered by copyright in countries that have signed on to the Berne Convention, but unless the person holds an actual copyright registration, they are not entitled to seek statuatory damages for copying of their work. Also, the US rejected one article of the Berne treaty, which was the recognition of moral rights to a work, and so does not give copyright holders the right to object to their work being distorted, mutilated or modified in a derogatory way that is harmful to the original owner's reputation. Their reasoning was that derogatory use of a copyrighted work was acceptable under the 1st Amendment as freedom of speech. So you couldn't copy someone's character and use it yourself, but you could take their character and use it in a parodic or derogatory manner and that would be fine, so long as you and the original owner are both US citizens and the work was created in the US. Also, the US allows transformative appropriation of other people's art to create a new work so long as it doesn't significantly infringe on the original (mainly in a commercial sense) - in the Commonwealth this is not permitted and works can only be appropriated or transformed for things like criticism or academic study, not profit. So if you're a US citizen, unregistered copyright only gives you protection from theft or copying of a significant portion of the original work for commercial or competing purposes, and only if the overall work is clearly intended to have the same impression on the intended audience as the original, and the burden is on the original owner to prove that there is substantial similarity, that the copier had access to their own original to copy it, that they made use of that access, and that there was significant infringement upon their rights (otherwise it will be dismissed as 'trivial use', which is permitted). Yay for law studies.