Previous response is correct.... that's a hair or something on the sensor.
Actually the sensor has a filter over it, and that hair (or whatever) is on that.
And, I agree... it's best to try using a puff of air from a "rocket blower" or similar. If you look up one of those online, you'll find them. Shooting with a digital SLR, you should have one in your camera bag anyway, for quick sensor cleanings. Once you have a bulb blower of some sort to use...
First thing to do is make sure your camera's battery is charged up before trying to clean it.
Then remove the lens.
Turn the camera on, go into the menu, and select Sensor Cleaning. As mentioned, this will lift the mirror up out of the way. It also will prop open the shutter, revealing the sensor behind it. Note: Be extra careful around the mirror, focus screen, shutter and sensor. They are all easily damaged. Try not to touch anything. That's why a puff of air from a bulb blower is the best course.
Once the camera is in the manual sensor cleaning mode, hold it face down and gently give one or two puffs of air from the blower up into it. You don't need to stick the bulb blower into the camera. Hopefully this will dislodge the hair and allow it to drop out of the camera. Work quickly because as long as the shutter is being held open and the mirror is being held up out of the way, there is drain on the batteries. This is fine for a little while, but after 15 minutes or half an hour the battery might run down enough that the camera shuts down, closing the shutter and dropping the mirror.
When done with the cleaning, turn the camera off to take it out of the sensor cleaning mode, close the
It is possible the hair (or whatever) is too adhered to the surface to puff away with air. If so, a Speck Grabber can be used to remove a single speck..... But really a proper "wet" cleaning likely is what's needed.
Read these two websites thoroughly about doing sensor cleanings yourself: http://cleaningdigitalcameras.com/ and http://copperhillimages.com/. You will have to buy several items to do this sort of cleaning.
Alternatively - say if you don't feel comfortable doing the deeper sensor cleaning yourself - you can send the camera to Canon's Service Department. Or, particularly if your camera is out of warranty, you might find a local camera shop tthat will clean the sensor for you.
p.s. That's almost certainly not something on or in the lens. Particles on or in the lens simpy cannot show up that distinctly. At most, a lot of particles in or on a lens might cause more flare than usual or cost a little resolution. But you rarely will see it in images.
Also you don't have to worry about anything you see through the camera's viewfinder. That will be on the mirro or focus screen, and will not appear in your images because the mirror flips up and covers the focus screen during exposure, before the shutter opens and uncovers the sensor. So anything you see through the viewfinder is merely a nuisance. I don't recommend tying to clean the mirror or focus screen... they are both easily damaged (and costly to repair). The safest thing to do is leave these alone until you can have the camera properly cleaned.
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Alan Myers
San Jose, Calif., USA
"Walk softly and carry a big lens."
GEAR: 5DII, 7D(x2), 50D(x3), some other cameras, various lenses & accessories
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