Any camera with interchangeable lenses has the potential for dust to stick on the sensor, and even with modern anti-dust self-cleaning sensor occasionally the inevitable happens.
Recently I rather foolishly managed to pick up my GX7 with no lens and managed to get a finger-print right on the sensor itself; some gentle wafting with a lint-free cloth just proceeded to move the print around and while some progress was made there was plenty of evidence of the residue when taking shots with a small aperture (f16-f22).
Here I shot a blank wall at f22 and the evidence is clear:
Shooting at a small aperture makes the spots far more noticeable, while a large aperture (f2-f4) hides the problem, it’s not always possible or desirable to shoot with the lens open.
After much investigation I settled on green swabs from Visible Dust; while a little expensive (£20 for 4 swabs) they seemed to have a good reputation.
These turned out to be a really simple solution, a small amount of the cleaning fluid is added to the swab and with a smooth wipe most of the dust was removed. One particularly obvious mark actually turned out to be a piece of dust on the rear element of the lens which was cleaned with a lint-free cloth.
The final results seems much better, there are still a few spots so I may have another try in a few days to get the last few stubborn leftovers.