My daughter wanted to be Mona Lisa for Halloween, so this is what we came up with. It basically consists of two parts, the dress and the frame/picture.
First you need to make the dress. Depending on your closet, you may be able to pull out something that could work. We used a McCalls sewing pattern (MP343, to be exact) and an appropriate dark brown fabric to create the dress.
After picking your fabric, follow the directions for your sewing pattern to complete the dress.
Cut a small hole into the foam core side pieces. Feed one end of the elastic through and tie a knot to hold it in place. Repeat for the other side.
Attach the front end of the elastic to the opposite side of the gold frame (to the back of the gold frame - see image) I used straight pins through the elastic into the edge of the foam core.
Now that you have an "X" of elastic, we need to add one more piece to keep the frame sitting on your shoulders.
Sew a six-inch piece of elastic to the other two. The goal is to form a triangle for the head to go through.
For my daughter, I needed to attach the elastic "X" to the background image. To do this, reinforce the paper with some duct tape, and sew the elastic to it.