After the ceremony, the registrar will normally ask the photographers not to take any pictures during the signing of the wedding register.
This is to prevent any distraction during the signing. Also, as the wedding register is a legal document, it can contain sensitive information which wouldn’t be appropriate to make copies of.
The registrar will normally use a pretend book to pose with once the signing is complete. These photographs can involve just the bride and groom, as well as some other members of the bridal party.