Does intentional nocturnal emission invalidate the fast, when caused by looking at pictures, and does it necessitate making up the fast and offering expiation?

You must repent to Allah for intentionally looking at what is forbidden. Allah is aware of you, and His gaze upon you precedes your gaze upon what you look at. Lowering the gaze brings sweetness, tranquility, and peace of heart. Allah Almighty says: "Tell the believing men to reduce [some] of their vision and guard their private parts. That is purer for them. Indeed, Allah is Acquainted with what they do." (Quran 24:30). Wet dreams do not invalidate the fast because the pen is lifted from the sleeping person, and you are not required to make up for that day.