Look closely at the blue sky. Upper left corner has 3 sensor spots and on the right just above the clouds are 3 more. Dust can collect on our sensors when a lens is removed. The dust spots are most visible in highlight areas. You can confirm the problem by viewing other photos, shot since your last cleaning, to notice the spots in the same position pic after pic. Spot removal tool easily solves the problem in a finished photo but having your sensor cleaned eliminates it for a time. Very nice shot of Biltmore...makes me want to go back again.