If you press Shift-pause or alt-pause (I forget which) it does a special kind of pause of the game. Then you can press enter and exit the cockpit of your craft and use flight controls to move around. With that you can take screenshots without any interference from the HUD, and you also get the benefit of being able to take a picture from any location and any angle that you want. But this feature is only in SCP.
I tried this, and to be honest, I was somewhat disappointed. Instead of being like spectator mode in MP without the HUD, it was just 3rd person free camera but paused. I think this feature would be

better if it worked like spectator mode. Is it possible to put this into the source code, and if so, would the coders be willing to do so?