How accurate of a effect do you want to create? For a simple reproduction, just layer a grid of black lines (horizontal + vertical) over the image. To go even further, you'd want to also duplicate the sub-pixels of the screen (red, green and blue). To see what I mean, get a good magnifying glass and look over your LCD (or even your CRT) screen.
This article (primarily page 2 and 3) describes the basic structure of LCDs. And the Wikipedia pages on
ClearType and
Subpixel rendering have some nice pictures of an LCD's sub-pixels.