The United States is unique in requiring that you register photographs to gain effective copyright protection. You should therefore consider registering your copyright in your pictures in the United States if it seems likely that it will be infringed there.
Note that schemes offering to register works in any other country are, on the face of it, scams. You have copyright simply by virtue of creating a work. If you expect to need to prove the date before which the work was created, you can easily and cheaply do it yourself: post a copy to yourself using the Post Office "signed for" service, keep the receipts, and do not open it when it arrives.
For full advice on whether to register your photographs in the US, and if so how, see the link below.
Text © Mike Holderness & previous contributors; Moral rights asserted. The collection (database right) © National Union of Journalists. Comments to email@example.com please. You may find the glossary helpful.
The National Union of Journalists must not, can not and would not wish to dictate rates or terms of engagement to members or to editors. The information presented here is for guidance and as an aid to equitable negotiation only.
Suggestions apply to contracts governed by UK law only. In any event, nothing here should be construed as legal advice.