Sounds suspiciously like video card driver. Reinstall from the Desktop Application manager. Open an image, and if it has the problem, save as a JPG. Open the JPG in another application to see if the atrefact is still there.
If not, make sure your video card driver is up to date from the card maker's web site.
If you still have problems, what operating system? Upload a full res screen grab of your workspace showing the problem