Vignetting

Vignetting is a reduction of an image's brightness or saturation at the periphery compared to the image center. Through conversations with some photo profesionals, they said that its usually caused by exposing the limitations of the lens in print of film SLRs. This, in turn, creates a shadow-like black blur around the picture. It used to be an undesired effect from the limitations set by lens but now, its a commonly used boarder or effect to draw the focus to the subject of the photo. It can easily be duplicated in digital photos by 'burning' the peripheral of the photo.

(thanks to 'FDLensGuy' of Quezon City and RJ Palad for their insight on lens and stuff)