Copyright is automatically conferred by making the photograph so there is nothing to do. This is the standard position in most countries of the world that are signatories to the Berne Convention.

Some countries operate copyright registries where you may additionally record your ownership of copyright with the benefit of additional legal protection. EG registration with the US Copyright Office allows much higher punitive damages to be sought from infringers.

The UK does not currently operate a registry. This may change. Registration was a key proposal of the 2007 Gowers review of intellectual property law.