"Things" that are in the lense (scratches, fungus) don't create hard edged artifacts in your images... things on your lense will affect overall sharpness. Generally speaking, since I'm sure someone will bring up the one exception to this.
It's easy to check, swap lenses. Borrow one from friend or rent one from a store. Or, perhaps a store will be lend you one to help pinpoint the issue if you were going to use a store's repair services.
Are you getting the exact pattern on several images? Have you confirmed that it is not part of the background that the objects are sitting on?
If you are sure it's not part of the background then it's probably on the sensor. Have you ever cleaned your sensor? Could be the marks that a q-tip swab left...?
Update: Looked again... I'd bet money (a small amount) that it is the shadows left by tiny fine hairs (like lint) on the sensor. Look at the top of your sensor for little clumps of lint.