A vignette is a type of photo border effect where the photo gradually fades into the border background. The visible portion of the image remaining is usually in an oval shape.
In Photoshop, first open the image you want to add the vignette effect. Make a duplicare and close the original.
Next, use the Elliptical Marquee tool with a Feather value of 10 - 20 pixels depending upon the size of the image. Then, make an oval selection around the subject in the photo. While the marquee tool is still selected in the Toolbar, you can move it around by using the Left and Right or Up and Down arrows of your keyboard.
When satisfied, sace the Selection by clicking Select > Save Selection. Give that a name.
Then, Click on the "Create a new layer button" at the bottom of the Layers palette (next to the Trash Bin).
Then inverse the selection by clicking Select > Inverse.
Now choose a colour from the Swatches or Color palette, and fill (Edit > Fill) the inverted selection with your choice of color for the vignette border. White is a popular choice.
The oval subject portion now fades into the background colour.
"Save" to a different file name than the original photo and you're done. "Save As" to a JPEG format and you're ready to serve it on the Web!