Photo Album (spoilers)
So at the end of the film, he is going through the album Natalie made.
It starts out with their wedding photos and goes on to show pictures of Jack with all these different women, in intimate poses.
I interpreted it to mean that she was smarter than Jack and knew about all his affairs.
SO why did she photograph him with the women? I can see why she wouldn't want to confront him about it....like thinking he wouldn't stop anyways, being in denial, avoiding confontation, etc. But she knows about it, follows him, and photographs him cavorting with these women. Wouldn't that be painful to watch your husband with another woman? Or maybe she was just biding her time to leave him with his album of transgressions.