Copyright Watermark Questions

Hello!

I'm totally new to copyrighting my photographs and had a couple of questions. I may have a business opportunity to pursue, but before I send any images to anyone I want to do my due diligence and do what I need to to protect my work. From what I've researched you can put a watermark discretely on your pictures to deter thieves from taking credit for your work, but in order to receive genuine protection you have to register your images and pay a fee which doesn't seem worth the expense considering my small portfolio. Do any of you pay the legal fees to officially copyright or do you just opt to watermark? If you watermark, what do you write and how do you do this in cloud-based Lightroom?

Thank you in advance!