I was under the impression that everything you do is automatically copyrighted unless you explicitly waive your rights. This site seems to agree ( https://www.teachingcopyright.org/handout/copyright-faq ).

You can register your copyright, which helps (scratch that, according to the link above, is NEEDED) when fighting over ownership, but anything you make is copyrighted automatically. If you made something as an employee of a company, it's known as "work for hire", and belongs to them.

So, without a registered copyright, you may be out of luck pursuing them in court. You can look to see if you can register after-the-fact. From what I understand a Getty sale is often for very little money (a couple bucks is common, and a hundred or two a rare event). If you're only able to claim the lost sale as your damages, it might not be worth the time or effort to fight for it, unless you're just suing them to make a point.