Copyright arises automatically. Period.

There are some jurisdictional issues - in the UK for example the work must be reduced to a material form.

In the USA there is argument whether copyright is wholly federally pre-empted or whether common law copyright may subsist in relation to works that are not protected by federal (statutory) copyright. Nimmer (the great US authority on copyright) used to discuss (not sure about current editions) California cmmon law copyright protecting a tune that had only been whistled and not recorded.

What is being asked here is not how copyright arises, but how it may be proven (or evidenced) to have arisen (and when) and how first ownership may be proven (or evidenced).

And there is no such verb as "to copyright".

Bah.