Add Layer Mask
1. Open Photoshop. Open Image to work with "Add Layer Mask" button. Double click and unlock the Background layer. Check out the detail procedure here.
2. Click "Add layer mask" button. It is second from the left at the bottom of the layer palette.
3. Once you click it you will find that foreground and background colors become black & white. And the layer mask thumbnail added to the image layer.
4. Select brush tool. Keep black as a foreground color.
5.Since we want to create vignette effect, start painting around the sides of the image.
6. You will find that the image is as if erased but it's just hidden behind the mask. Painting with white will reveals the image behind the mask.