Originally posted by Guayabero However, here is what I do not understand. I ran a test to check for dusk and it came out clear. Is this one of them circumstances where a censor clean kit needs to be purchased?
An O-ICK1 sensor cleaning kit was one of my first add-ons for my K20D. I heartily recommend it. Your dust-check results seem to indicate that it's not dust, but maybe some dried moisture that doesn't show as dust; or a (shudder) sensor stain. In fact, what I saw on your image looks much more like dried moisture than dust. I'm not sure what sensor stains look like. What is your camera? How old is it? Is it still under warranty?
My recommendation: Get and use the kit. (It's good for many many many uses, on any dSLR.) If that doesn't fix it, see about warranty service. Good luck!