Marks on images

I have a small issue with my D70.
In any pictures that feature the sky predominantly three marks appear on the images, doesn’t matter what lenses I use the marks are always in the same place. I've marked the last one, but i dont think i needed to as the spots are so obvious.
These three below are really bad, probably the worst I have seen.
Is this dust? And if so can I clean it or should I get it done by a professional.
excuse the jpg compression, i'm on a modem at the moment.

In any pictures that feature the sky predominantly three marks appear on the images, doesn’t matter what lenses I use the marks are always in the same place. I've marked the last one, but i dont think i needed to as the spots are so obvious.
These three below are really bad, probably the worst I have seen.
Is this dust? And if so can I clean it or should I get it done by a professional.
excuse the jpg compression, i'm on a modem at the moment.


