SCP Foundation: Iris Through the Looking-Glass (Light Novel) Vol. 1

An unnamed boy encounters an inexplicable phenomenon - the same photo of a girl appears inside any book he opens. When one book in the library suddenly transports him to the SCP Foundation, a secret organisation dedicated to containing anomalous entities and phenomena, he learns that the girl's name is Iris - and that he's going to have to work alongside her to get them both out!