Vignette
A vignette is a subtle darkening of the edges of an image. It pulls the eye inward to the brightest part of the image.
Step 1: Select the Rectangular Marquee Tool from the toolbar and feather the radius to 200 px in the Options Bar.
Step 2: Click and drag a selection in the image just inside the outer frame.
Step 3: Invert the selection to the outer edges by pulling down the Select menu to Inverse.
Step 4: Create a Levels Adjustment Layer in the Layers palette.
Step 5: Adjust the Gamma (middle gray slider) to the right to darken the edges.