It's pretty simple in the US. A work has a copyright regardless of whether it's registered or a notice placed on the work. Registration provides easier means of

It's pretty simple in the US. A work has a copyright regardless of whether it's registered or a notice placed on the work. Registration provides easier means of asserting your copyright but you have a copyright as soon as you create the work. If I wrote a handwritten note about OpenAI on a cocktail napkin then I have copyright over that work barring some challenge to whether it's a "creative work" or not. It doesn't matter what the medium is, or how it's shared. The internet makes this challenging in that it's essentially a shared technical means of disseminating the work, but the work remains copyrighted no matter how publicly available it might or might not be. It's just a matter of the rights-holder asserting their right. Which is something NYT does with their paywall all the time.