Lots of users ask,
Can you tell me if it's OK to use screenshots and pics of the Master Chief and Halo 2 on my website?
Generally, if you’re an individual with say a noncommercial fansite or a blog, we have no objection to you illustrating that site with images that are freely available and designated for use and download in the Bungie.net gallery sections.  You aren’t allowed to use those images for any commercial purposes, including but not limited to use on a website that charges access or subscription fees, or reproduction on any items for sale.  You also are not allowed to change, alter or otherwise modify the images made available for use in the Bungie.net gallery sections, except for sizing the images.  You also cannot pass off any Bungie’s trademarks, logos, images, products or other materials as your own, and don’t use the materials in ways that would be illegal, libelous, or harm the reputations of Bungie and Microsoft.  Note that everything on Bungie.net is protected by copyright and trademark laws and we will take actions to protect them.
 
When you use something from Bungie.net, we ask that you provide a notice somewhere on your page which says:
 
“[Whatever you use – usually Bungie and/or Halo] are either registered trademarks or trademarks of Microsoft Corporation in the United States and/or other countries.  Certain materials are copyright Microsoft Corporation.
Also, Microsoft reserves the right to come after you if it thinks the use is unsuitable in any way. Happy fun times!

http://www.bungie.net/News/TopStory.aspx?story=weeklywhatsfeb11