When the standard was created for capturing video to the digital domain it was decided to go with a slightly wider frame than that on a pure analogue system. So the analogue to digital conversion starts a bit before the line transmission begins and a ends a bit after. 702 of the pixels entering the computer are image pixels, the nine pixels on either side are additional pixels.

Most DV cameras that I've tried, however, do use these 18 pixels as image carriers. But when you capture images from an analogue source these 18 pixels will be black. For instance, the image on the right is a combination of an image from my DV camera and the same image after I recorded it to VHS and back again. Notice how the black sides have been added and how much detail is lost in the image. The red box is a zoom in of the edge.