some people have very clean lens but still get the same "artefacts" though. It's a weird phenomenon. could it be reflection within the camera (between different pieces of glass or even between some internal parts)?
Re: White Spots in Pictures Taken by Digital Camera
Floating dust particles may cause white spots appearing at different positions on pictures taken by a digital camera using the flash. Dust in front of a subject reflects the strobe light and the image of the dust is captured out of focus.
Dust, snow, rain, pollen, condensation, or any small airborne particles may cause the same problem. This problem may also influence compact film cameras. This problem will occur on most compact cameras with on-board flash systems positioned very close to the lens.