At about one hour and fourteen minutes a flash is used on the woman and their is the distinctive crackle pop of a flash bulb going off. Flash bulbs were not invented till 1925.
The main character has obvious bikini tan lines during the ritual.
In the beginning of the movie when they walk up to the gate of the Rosewood Institute, the camera pans back and you can see a palm tree in the distance behind the building. This movie being set in Baltimore means that there would not be any Palm Trees there.