As a writer I have some [limited] knowledge of copyrights etc. I too have been told it is futile to try to 'protect' your photos online. On my site, e commerce, I really don't care if someone borrows pictures of items. I am there to sell. But I do care if someone uses the original artwork logo I designed and paid an artist to create for that site.
My solution is to Trademark my logo with a watermark that has tm in the text. Then on the footer spell out that the trademark belongs exclusively to Lady of the Lake Vintage Costume Jewelry. Since it is an original artwork conceived by me, it is unique and ripe for 'interperatation'.
Technically anytime you post text or images or photos, on paper or anywhere else, you own the copyright. And a trademark is something no one else can use. They can be registered if you really want to be air tight.
Then, if you really want to protect it, you can subscribe to an online service that tracks the internet use of your pictures/ logo. They alert you to any violations. I understand that the results of these 'trackers' have been used and stood up under courtroom scrutiny. A simple Google search should bring up firms that do this for an annual fee, tracking a given number of images for a 12 month period.
Hope that is somewhat helpful...
Norma