When you're working with old photos, or with new photos that you would like to look old, vignetting is often the trick that makes the difference. It gives that sort of cameo look as the portrait subject comes forward and the background fades to nothing. Here's an easy way to do it.
Draw an elliptical marquee around the portrait subject. Invert the selection so that the background is selected. Feather the selection by whatever amount looks right (Select→Feather). Use Edit→Fill and set the Background color to white, the blending mode to Normal, and the Opacity to 100%. Figure 21.26 shows the effect.
Figure 21.26 No more annoying backgrounds. (Photo courtesy of Peggy Ogan.)