Jeremy Nicholl says to register photographic images at the US Copyright Office. “The U.S. may be a Berne signatory, but in practice the USA has a dual copyright system: major protection and zero protection.” Unregistered images are still copyrighted, but the remedies are quite limited. Registration carries with it statutory damages of $150,000 per infringement, plus legal costs. Valuators of such assets need to ask one more question: Is EVERY frame registered?
Watermarking is a technique photographers hate. A strong one ruins an image; a weak one is too easy to remove. The best practice to protect value is to place copyright information immediately next to the photography.
Finally, if you catch an infringer, document it. Screenshots are useful, as is downloading the Web pages to capture the source code from the infringing site.
There is value in the IP of photography. Licenses in ktMINE reflect royalty rates of up to 10% of gross profit for non-exclusive use of photography. That value should be protected.