Step 1: Pick a photo
Choose a suitable photo. For a high key vignette make sure the surrounds have lighter tones and for a low key vignette choose a shot with a darker background.
Step 2: Make a selection
Select the Elliptical Marquee tool and click to the top of where you want the vignette to start and drag the shape out until it surrounds your subject. When you let go you'll have a circular line of 'marching ants' which you can click in the middle of, holding down the mouse, to move it around the photo.
Step 3: Inverse
At the moment our subject is selected but we want to inverse this and select the background. To do this go to Select>Inverse. This will now have caused the 'marching ants' to surround the outside of the photo as well as your subject.
Step 4: Feather
If we created the vignette without feathering the edges of the selection it would be too hard so to soften it go to Select>Modify>Feather. The bigger the image you're working on the larger the amount you enter in the Feather Radius box will need to be.
Step 5: Create the vignette
The quickest way to create a vignette is to click on the black & white circle at the bottom of the layers palette and select hue/saturation. You can go to Image>Adjustment>Hue/Saturation but by creating an adjustment layer you can continue to edit your vignette after you've applied the changes. When the new window opens, drag the Lightness slider across to the right if you want a light vignette and to the left if you want a dark one. The more you pull it to the right the lighter it will be and the more you slide the marker to the left the darker the vignette will get.
That's all there is to it.
To see how we converted the colour image to black and white see our tutorial on Gradient Maps
Above: Light Vignette.
Above: Dark Vignette Added.