Found a chair back that looked liked it could have came from the time period and scanned it at the correct size to fit (600ppi). Trimmed away the background and moved it onto the Cleopatra file. Moved the chair layer below the Cleopatra layers to put the chair behind the body. Using the move tool the chair was moved to a position that looked right. With the chair layer still the active layer, the levels were adjusted to match the figure. The dodge and burn tools were used to bring out the details in the chair.
At this stage the chair looked pretty good, but it would look more realistic if it got darker and lost detail as it gets closer to the body. To get that effect, we used the lasso tool to make an irregular selection of the chair where we wanted it to get darker. Featured that selection by about 60 pixels and saved the selection to a new channel. Opened the channels palette and adjusted the selection as needed. Open the layers palette and put a new layer between the body and chair, then loaded the selection just made. With the gradient tool set to foreground to transparent, and black as the foreground color, filled the selection (It may take a few attempts to get the correct angle, just hit command z and try again.) After a nice gradation had been achieved, removed the selection and changed the layer blending mode to overlay and adjusted the transparency. Satisfied with the look of the new shadow, the chair and shadow layers were merged together.

TIP:
Get a good camera and photograph your own reference as often as possible. This will give you more control, for instance, staging and lighting the subject to fit the need. Rely on stock photos and you're at the mercy of what you can find.