I have noticed in pictures with a lot of white area that I get this image inside my picture, it only appears on white images and looks like in a fairly close zoom mode shot, note the round "fisheye" in this close up of a section of white wall mounted gutter downspout on my house.
well, of course the obvious question, have you cleaned the lens? And you see this in all your pictures always in the same location not just white, which makes it easier to see?)
My first guess is something on the lens as it doesn't look like bad pixels or a bad sensor.