Burn Your Vignette
In order to burn the sides, you'll need to employ a favorite trick of mine: Choose Select, Inverse to swap the selected and unselected parts of the photo. Choose Enhance, Adjust Lighting, Levels. Drag the black-point marker all the way to the right so that it is in line with the white-point marker.
To get rid of the distracting selection marks, choose Select, Deselect. Finally, you can put the finishing touches on your photo by cropping it to size. You might end up with something like my final version, above.
You can try for a similar effect by dodging the edges of your photos. Look for images with light backgrounds and shift the edges into pure white.