We have an older home ('25) with picture rail molding and plaster walls (you can't put nails in the walls). We have to hang things just like in this picture with picture rail hooks. I just ordered our hooks today! Little Green Notebook: Picture rails.
Decorative Picture Rail Hooks - Picture rails are strips of molding that adhere to walls and run horizontally around the room, typically aligning with the tops of any windows. This type of molding was once an elegant way of hanging artwork on hard-to-penetrate plaster walls. For an art collector who often rotates works, rental houses and apartments with frequent tenant changes, and those who simply like walls free of nail holes, picture rails offer a practical solution.