This is clearly an issue with the graphics board. If it only occurs on one application, the issue could be application specific; but if you see it in other situations (like video playback), it may be a hardware problem.
Have you noticed this in other situations? Do higher temperatures exacerbate the problem?
the problem occurs only with the "preview" and only with certain images. for example the following images found on the web http://xoomer.virgilio.it/mikimeta/Upload/Images/spiaggia% 20Meta.JPG, if scaled in size and regulated in the color creates the problem. for the rest nothing found until now with other applications