Guide to getting high-quality/big screenshots:
- Start a game for the map you want to show.
- After starting it, end the game.
- Go into theater mode and start the game.
- Pause it and take pictures (Press "X" and select the camera icon).
- Go on the internet to your service record (on Bungie.net) and take a look at your recent pictures.
- Click on "View in High Res" for the ones you want to use, and download them to your computer.
- Upload them to a photo site, like TinyPic - Free Image Hosting, Photo Sharing & Video Hosting.
- Highlight the link under "IMG Code for Forums & Message Boards" (for Tinypic.com) and post it on the thread.
- Your pictures should come up large and in high quality.