What must I do to rectify my error after having photographed school textbooks that had "All Rights Reserved" written on them, instead of buying them?

You proceeded with what you did out of ignorance that taking pictures of it was prohibited. Caution and a means of absolving oneself is to refer back to the responsible authority to seek permission from them or to pay financial compensation to them, due to the Prophet, peace and blessings be upon him, saying: "Leave that which makes you doubt for that which does not make you doubt."