Dirty sensor?

I took my 20d and kit lens on vacation (plane and cruise) without changing the lens and noticed this spot, just right of center. The spot persists but seems to be getting lighter. Is this condensation that will eventually clear up or do you think the sensor has to be cleaned?
http://members.aol.com​/steve547/spots.htm

It's a speck of dust, which will show up more clearly at a higher f-stop and on a bright blue sky. img00001 and img00002 are at f22 and f20, while img00003 is at f13. If you carefully look at img00001 in Photoshop you'll see lots of spots from dust (I counted 22). The one you are noticing in the middle is just the most predominant one.

Get a Rocket blower and follow the cleaning instructions in the camera manual. If that doesn't take care of the spot then you will need to do something like the Copperhill method to clean it.

Looks like dirt on the sensor. The reason it became lighter in the photos you posted is because of aperture settings. The smaller the aperture the darker and sharper the speck will appear. Your first photo was shot at f/22 (very pronounced) , the second one at f/20 (speck less pronounced)) and the third one at f/13 (just noticable).

Bob_A types faster than me.

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Thanks Bob and Wolf. The camera is only a few months old and I guess it has had dust on the sensor for a while, but I don't shoot much landscape or sky pictures and never noticed till I took it on vacation. I took about 300 pictures, but only a few had alot of sky, so the other 200 or so still look great. I'll start looking into that Rocket blower. Thanks again for your help

These are usually easy to remove from the images in Photoshop using the clone tool.