vignetter

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A device used to print photographs and illustrations with borders that fade gradually into the background.
• noun One who makes or specializes in the making of vignettes.

from The Century Dictionary.

• noun In photography, any device for causing the edges of a printed part of a negative to fade away evenly and gradually into the background

from the GNU version of the Collaborative International Dictionary of English.

• noun A device used by photographers in printing vignettes, consisting of a screen of paper or glass with a central aperture the edges of which become opaque by insensible gradations.
• noun A maker of vignettes.