Go to Forge mode with at least one other player and spawn a turret. Have the player that will leave the level get on the turret while the other player grabs the turret, then go to an invisible wall (for example, the ocean boundary on Valhalla). Put them up to it whilestill in the turret and still holding it. You may push the other player through the barrier. If this happens, have the person on the turret press D-pad Up to turn into the Monitor. If the player does not get pushed through the barrier, put the person in the turret as close as you can to the invisible wall. Then, have them look up and press D-pad Up. Afterward, have the person that is not outside the level quit. The person outside the level should commit suicide in Monitor mode by going far outside the boundary. Then, go to Theater mode and advance to the point where you killed yourself, and press Y to go into free cam. You are now free to take screen shots as desired. If you do not want to keep fast-forwarding through the game, record the last moments where you die, and save that for future use.
To go through walls and fences, go to any map (Foundry is recommended) and sapw a Machine Gun Turret or Plasma Cannon. Put the weapon on the side of the wall, get on, and then turn left, then up. After, that turn to a "Guilty Spark". Turn back to a Spartan or Elite.