In case you still don't know, just hit the tilde button (`/~) to go into hax mode, then type "tm" (without the quotes; stands for toggle menu) into it. You will then need to press the ~ key again. All the menus will be gone, so it may take some getting used to, but all your screenshots from then on will be menu free! When you want the menus back, press the tilde button again (nothing will show up, but it will still be in hax mode, don't worry) then type tm into it again. Then, tadaaa, you're back!
If you already knew all that, then sorry, I just felt like sharing. Adventure on, dovahkiin! c: