I have no idea whether these are indeed official, but they certainly appear to be some actual concept art matching what we saw in the teaser poster last month. They were posted on the SHH Forums by "Verbal21", and I'll be sure to update the article as soon as we either have any more pictures or confirmation of their authenticity. Thanks to CBM's own TheBlackWidow for the heads up.
With an all star cast which includes Chris Evans as Captain America, Robert Downey Jr as Iron Man, Chris Hemsworth as Thor, Mark Rufallo as Bruce Banner, Jeremy Renner as Hawkeye, Scarlett Johansson as Black Widow, Cobie Smulders as Maria Hill, Clark Gregg as Agent Coulson, Samuel L. Jackson as Nick Fury and Tom Hiddleston as Loki,
The Avengers is set to be released on May 4, 2012!