Thanks for the suggestions, but I've already done all that. The CCD is definitely damaged. Someone attempted to clean the CCD with something that left permanent indentations on it. It looks like dust, but it's not. Whatever was used in the cleaning attempt also left a large scratch on the CCD that shows up near the top of the photos. If you look carefully, you can see it on some of the photos. Fortunately, I can use digital editing cropping to remove or minimize the effects.
EDIT: To be accurate, I should say that the indentations and scratch are in the glass covering the CCD, not on the CCD itself.