In Ulster, specific photo ID is required in order to vote. If someone doesn't have any, they can apply for a free Electoral Identity Card.
"Applications may be made in person at the Electoral Office (see Contact Us page) where your photograph will be taken for the card free of charge (you will not need to provide identification if you apply in this way, provided you are listed on the electoral register). You will need to provide your National Insurance Number on the form. You must make an appointment to apply for an ID card in person."