We have an older home 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.
NY Good Questions: Best Way to Hang Art from Rail Molding?
Create a multilevel display with our Studio Wall Easel. Frames are secured within a pair of brackets or hung from a picture hanger; brackets and picture hangers slide along the hanging pole and lock into place.
Modify a piece of common molding to make a picture rail. Decorative golden picture hooks fitted with chain and rope display a mix of frames and add architectural interest. Use a circular link at the top of each chain to hang it over the hook.