Continuity mistake: When Sy is following Nina and Jake after he put the picture of the husband cheating in with Jake's pictures, the cars pull over to the side of the road. If you watch when they pull over, you see that they pull over next to a down sloping hill that is nicely green with grass and a few sporadic trees. But when they show Sy's car in the rearview mirror, you see that they are now pulled next to a large up sloping hill that is covered in leaves, dirt, and a lot of trees. (00:53:40)
Chosen answer: This is mentioned on the DVD commentary - it's deilberately open ended so one can interpret it as either it's Sy imagining what he wants to happen OR it's what really happened.
Neil Jones
As Neil Jones said, the ending is open for interpretation. However, I think there is reason to believe that Sy imagined the photo. It shows him and the family outside of their house, all looking happy together. Would they want to take such a photo with Sy after the incident at the hotel? And before the incident, they were probably not close enough with Sy that he would be in a photo taken at their home. Him and no other guests/visitors.