Image retention is not the same thing as screen burn.
Screen burn is permanent. Image retention is not.
Screen burn is where the phosphor in one part of the screen has been worn away at an accelerated rate compared to another area.
Image retention is where some latent energy is radiated after the main image is gone. It is, if you like, a similar effect to you get when dazzled by a camera flash.
Please don't panic people in to thinking that image retention is the same as permanent phosphor wear. thanks.
DannyW, it very much depends on the TV's contrast setting. Contrast makes the lighter parts of the image brighter. Taken to extremes this can cause screen burn. If you are worried at all then try using the TV on Eco or Theatre modes or the equivalents for your set.