A Spanish children's welfare organisation has launched an innovative poster campaign that can only be seen by children.
Using lenticular printing - a technique which means different things are seen by people viewing at different angles - the Anar Foundation have put 'secret messages' on billboards containing a phone number for a children's helpline.
The organisation said the number would be clearly visible to a child, but would not be within the eyesight of an adult. It said the lenticular printing would help children gain confidence to call for help, particularly if they were in the company of their abuser - if the helpline number was clearly visible to the adult, they might then say things to put the child off reporting them.
The BBC reports that the 'secret' message reads: "If somebody hurts you, phone us and we'll help you."