Those shots appear to have originated from Bungie's own forums, reposted at Bungie.org and finally at NeoGAF, offering a look at what may be Reach's arsenal, locations and maybe even a few unannounced features. It's unclear whether these shots are from the multiplayer beta promised to those who pre-ordered Halo 3: ODST, but since one shot shows a menu screen offering access to a Solo Game and Activities, we're wagering it's a portion of the campaign.
They're certainly not what we'd call quality shots—it's doubtful that Bungie or Microsoft would be pleased about the leak, given their quality—but at least it gives the hardcore Halo fans a taste of what to expect when Halo: Reach ships next year.