"One of the most frequent questions I see posted in digital photography forums (second only to "what's the best digital camera...") is "what are these marks on my images". The answer is invariably that they are marks resulting from dust on the sensor of a digital SLR. The Olympus DSLRs have an ultrasonic "dust shedding" function which seems to keep them more free of dust, but all Canon DLSRs from the Digital Rebel, through the Canon EOS 20D and (presumably) 5D to the Canon EOS 1D series cameras suffer from occasional dust issues. The same applies to Nikon, Pentax and Minolta DSLRs. Eventually all of them will need to be cleaned."Aha, fresh from the previous article on cleaning your lenses, here is one on cleaning your sensor. So I honestly feel that dirt on the sensor causes many more problems than a dirty lens. However, cleaning a sensor is much harder and is much more risky. The solution suggested here only removes dust particles and won't won't remove grease or oil or other "non-dust" crud on the sensor, but that's another story.