Image “persistence” is kind of an interesting new phenomenon we’re seeing in LCD displays.  At first, it may seem like the old “burn-in” we saw on the old CRT monitors, but it behaves more like ghosting- an image seems to leave a trace that fades within minutes, or hours, or an image that may be barely visible when the overall tone of the display changes.  It’s caused by the same thing that caused burn-in…  leaving the same image up on the screen for too long…  but fortunately, on an LCD display, it’s not a permanent problem. 

Burn-in on a CRT is actually a break down in the phosphors of the screen.  Image persistence on an LCD or LED is more the “memory” of the liquid crystal- the part of the display that actually filters the light, pixel by pixel, to create the image.  The fix is to force the LCD to display a wide range of it’s native colors, essentially shocking each pixel back to it’s normal range.

There are a few solutions to this, probably the easiest and most effective is the JScreenFix Java applet, from the JScreenFix site, here.
The JScreenFix applet runs a fast and furious pattern of red, green and blue to push each pixel back to it’s original response state (besides being somewhat hypnotic to watch).  On that site there’s also some interesting stuff- dealing with dead pixels on an LCD by “massaging” the spot, also a range of other display-related resources. 

All good stuff, but the bottom line is the same thing we’ve been told all along.  Preventing the problem by using a good screensaver (one of the best solutions is one of the easiest- just running a slideshow screensaver with many varying images with a good range of colors and contrasts), and avoiding the same displayed image for lengthy periods of time (and this includes toolbars and workspaces from your most-used applications).