The only scenes that were not real was when Cy was in their house, and they come back and treat him like Uncle Cy - a part of the family.
Near the end of the movie, when we are back in the interrogation room, he asks Dr. Benton if he was a good man. Cy then answers it himself and has kind of a breakdown – he starts to cry and says stuff like “I can tell you’re a good man. You would never do things like make your children pose for disgusting pictures…”.
From that scene, it seemed to imply that Cy himself was a victim like that, whereby someone (like a parent) took kiddy-porn photos of Cy. This caused him to be socially messed up in life, and also gave him sort of an obsession with photography. He longed to be part of a normal happy family, and after seeing pictures of this particular family, he “adopted” them as his own. When he saw pictures of the husband having the affair, he felt betrayed all over again, and was enraged at the guy. Cy went to the hotel because he wanted to punish and humiliate the guy, just like Cy had been abused as a child. (He also used photography as a weapon when he took pictures of the little girl and sent them to the store manager - Cy himself wasn’t a pervert, he just wanted to scare the guy who fired him). He wasn’t using film in the hotel room because he didn’t have any interest in actually having the photos, he just wanted to punish the husband (and vent frustations against the person who did it to Cy as a child).
Earlier in the movie Cy talked about the fact that children take different types of photos than adults take. Adults take pictures of major events, and kids take pictures of ordinary things around the house and yard. Those were the types of pictures that Cy had in his camera (and at the end, he seemed pleased to see them). So it seems that Cy is always stuck in childhood, in a way.[/spoiler]