It's dust on the sensor, take a turkey baster and blow air on the sensor. DO NOT USE YOUR MOUTH nor should you use compressed ai as it is too powerful. Just put your camera on sensor cleaning mode, th emirror shoulf flip out of the way, and the shutter open, with the lens removed, and the front of the camera facing down rise the turkey baser up into the amer (do not touch the sensor) and blow a few burst of air thoroughly around the sensor. Then, keeping the camera facing down, turn it off and let themirror and shutter close. then replace the lens.

http://www.youtube.com/watch?v=UPrxXcwSpDE