Screen ghosting issues

I have Nov 2012 Imac which has started showing strange screen artefacts. If I leave an object on the screen such as Safari without moving it for a while (say 20 mins), it leaves a greenish ghost image after I close or move the application on the screen. This can take a while to disappear.

Has anyone else noticed this? Is this something that I should be worried about, or can it be stopped by simply changing a screen setting somewhere?

Any help is appreciated.

 

Ah yes, I've managed to find some threads regarding this now. Mine doesn't appear as bad as others but could need to be replaced anyway.